EM guidemap - Low back pain

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Introduction

 History of the present illness

Examination

Diagnostic testing

Medical decision-making

Appendix

Introduction

- although the majority of patients who present to the ED with low back pain have a self-limited back strain or an acute exacerbation of a chronic-back-pain syndrome, an EP should always use a consistently methodical (? step-wise) diagnostic approach that specifically considers, and excludes, potentially serious pathology so as to avoid "missing" a serious cause of low back pain

- this guidemap is tightly focused on the "red flag" approach to a patient with low back pain - to ensure that serious causes of back pain are considered, and diagnosed, during the ED visit

- this guidemap does not discuss the management/treatment of diseases that cause low back pain - it merely offers a diagnostic algorithmic approach to the ED evaluation of low back pain

- this guidemap does not contain any information on the diagnostic evaluation of less serious musculoskeletal causes of low back pain, and the reader should consult EM textbooks and other informational resources for further details about how to use a pattern-recognition approach to diagnose those entities

History of the present illness

- it is important to first determine when the low back pain started, how abruptly the pain started, and whether there were any precipitating postural factors, and/or sudden twisting movements, and/or weight-lifting elements at play at the time of onset of the back pain

(* sudden pain in the low back temporally related to heavy lifting - especially a rotational movement with the patient holding a heavy object away from the central axis of the body in a long-levered postural position - is most likely due to benign musculoskeletal pathology or a herniated disc; minor twisting body movements may be a precipitating factor in disc herniations and it may even produce a compression fracture in elderly or osteoporotic or chronic steroid-dependent patients, or it may be a "red herring" phenomenon that has no real etiological relationship to the sudden back pain)

- low back pain that is distinctly worse (or better) when assuming a certain posture or peforming a certain movement suggests a musculoskeletal etiology; while a writhing or restlessly pacing patient, who cannot get comfortable and who does not want to remain still, should be presumed to have back pain of non-musculoskeletal etiology eg. renal or biliary colic, a distending or leaking or rupturing AAA

- determine exactly where the pain is situated, whether the pain is very localised or diffuse, and whether it radiates to the buttocks or thighs or abdomen or below the knees - determine whether the patient has a history of similar pain and whether the etiology of the pain had been previously established (and by what means - CT scan or MRI), and whether the present back pain episode is identical to the previous episodes of back pain

(* if the character of the back pain + it's pattern of radiation + its associated/aggravating factors is identical to previous episodes of a known "benign" cause of recurrent low back pain => no further ED-based diagnostic workup may be required)

- in patients with chronic low back pain => determine the functional limitations of the patient and the analgesic drug use pattern

- specifically inquire about the presence of any of the following "red flags" suggesting potentially serious lumbo-sacral spine (or other) pathology
 

Red flags suggesting potentially serious lumbosacral spine (or other) pathology
  • sudden onset of severe back pain, +/- abdominal pain, in an adult > 60 years (? symptomatic AAA)
  • "colicky" pain associated with visceral functional symptoms, or "writhing" pain behaviour
  • severe, unrelenting back pain that is worse when supine, and/or worse at night preventing sleep, and/or resistant to postural modification or high dose narcotic analgesics
  • persistent, unremitting back pain of any type (> 6 weeks duration)
  • any new neurologic deficits (lower extremity weakness or paralysis, saddle anesthesia and decreased anal sphincter tone, lower limb sensory loss or numbness, urinary retention or overflow incontinence, rectal obstipation or incontinence, erectile dysfunction)
  • bilateral neurologic deficits or neurologic deficits involving multiple root levels
  • any previous history of cancer
  • any history of unintentional weight loss (> 10 lbs in 3 months)
  • any history of fever or night sweats
  • any history of an immunocompromised state, immunosuppressive drug or chronic steroid use
  • any history of IV drug abuse
  • any history of a bleeding diathesis or anticoagulant drug use
  • any known AAA or previous aortic graft surgery
  • any known underlying bacterial infection eg. pyelonephritis
  • any known valvular heart disease, valve replacement surgery or a previous history of endocarditis; any new-onset heart murmur +/- fever
  • any known active PUD/pancreatitis
  • any recent major trauma or penetrating trauma
  • any recent spinal anesthesia or spinal tap
  • any recent back surgery

- inquire about gastrointestinal and urinary symptoms and gynecological symptoms that may suggest non-spinal (intra-abdominal) pathology

(* do not automatically presume that the combination of suprapubic discomfort, urgency and urinary frequency implies cystitis; suprapubic pain could be due to bladder spasms, which are secondary to an early epidural compression syndrome, and the combination of suprapubic discomfort + urinary urgency + decreased urinary stream may reflect early bladder nerve compression, which may precede the development of frank urinary retention in patients with an early epidural compression syndrome)

- a psychosocial history is often necessary if the patient has a history of recurrent back pain and multiple ED visits, or a history of "doctor-shopping"

Examination

- check the vital signs for cardiovascular instability (suggests a leaking AAA) or a fever (suggests infection or malignancy or a rheumatological disorder)

- emaciation suggests an underlying malignancy or an immunocompromised patient

- examine the skin in all febrile patients for evidence of a source infection eg. cellulitis, "skin-popping" abscess

- examine the heart and lungs prn if mid-upper back pain is present (possible PE or AMI or aortic dissection), or if endocarditis or pneumonia or an underlying malignancy is suspected

- examine the abdomen in all patients > 50 years of age for evidence of a pulsatile mass, bruits and weak/missing femoral pulses

(* an abdominal exam has a low sensitivity for an AAA, and the triad of abdominal pain + pulsatile mass + shock is found in < 25%  of cases; diminished femoral pulses are rare and distal pulse deficits secondary to peripheral emboli from an intramural thrombus is an even more rare physical finding)

- examine the abdomen of all patients, who have a history of associated abdominal pain (or prominent abdomino-pelvic visceral symptoms) for any abdominal tenderness or masses

- a rectal exam is selectively indicated to check for rectal sphincter tone (if a cauda equina lesion is suspected), to check for a rectal/prostate carcinoma if an underlying malignancy is suspected, or to evaluate the prostate if prostatitis is suspected

- a pelvic examination is selectively indicated when pelvic pathology or an underlying malignancy is suspected

- inspect the back for any areas of redness or bruising or swelling or deformity or previous surgical scars

- palpate and percuss each vertebrae for point tenderness if the pain is localised to the spine or central back, or if infection/neoplasm is suspected

- limited ROM of the spine strongly suggests a musculoskeletal problem, but is of very little localising value

- check the ROM of the hip to exclude referred back pain secondary to hip pathology

- point tenderness over the ischial tuberosity or greater trochanter may be the only clues to localised bursitis

- perform a straight leg raising test in patients with a history suggestive of sciatica (lower limb pain that radiates below the knee)

(* see the appendix for details on how to perform and interpret the straight leg raising test)

- perform a brief/detailed neurological examination of the perineum and lower limbs - a scrupulous neurological examination is mandatory if there are any neurological symptoms, or any abnormal neurological signs, or if there are multiple risk factors for any pathology that can cause an epidural compression syndrome

(* a minimal screening neuro exam would include hip flexor strength (L2/3), knee extensor strength (L3/4), foot dorsiflexion strength and/or heel walking (L5), plantar flexion strength and/or toe walking (S1), knee reflex (L3/4), ankle reflex (S1), anterior thigh light touch sensation - both upper (L2) and lower (L3), medial foot sensation (L4), dorsum of the foot sensation - just proximal to the web space between the second and third toes (L5) and lateral foot border sensation (S1) +/- peri-anal sensation (S2-4) +/- rectal sphincteric tone (S2-4) => detailed light touch, pain/temperature and proprioceptive testing can be reserved for selective cases when there are neurological symptoms suggesting a spinal cord or cauda equina syndrome - see the appendix for a detailed sensory dermatome map and motor testing)

- palpate the distal pulses and check the capillary perfusion of the toes if the patient's clinical history suggests effort-claudication (when a patient complains of buttock/lower limb pain that is precipitated/aggravated by ambulating and relieved by rest)

(* clinical evidence of arterial insufficiency of the lower limbs suggests "vascular claudication" and may help differentiate that entity from "neurogenic claudication" secondary to spinal stenosis; patients with spinal stenosis also have increased pain when hyperextending the back for > 30 secs and significant pain relief when stooping; spinal stenosis patients may have no pain when exercising in a flexed position eg. riding an exercise bicycle, but they may have disproportionate pain when descending steep hills in a hyperextended position)

- perform a Wadell evaluation if the clinical history suggests non-organic disease

(* see the appendix for details on Wadell's criteria)

Diagnostic tests

Plain film X-rays of the lumbar spine

- are rarely indicated in patients with back pain of acute/subacute (< 4 weeks) onset unless there is a history of major trauma

- may be indicated as a cheap screening test in "red flag" patients with acute/subacute back pain + suspected spinal infection or tumor

(* however, plain film X-rays have a low sensitivity and cannot be used to exclude those possibilities => in the patient with multiple "red flags" other imaging studies, such as CT scan or MRI, are indicated even if the plain film X-rays are negative)

- the use of plain film X-rays to screen for spinal degenerative changes, congenital anomalies, spondylolysis, spondylolisthesis and scoliosis very rarely adds clinically useful information => the presence of degenerative changes rarely correlate with the presence of symptoms, while other abnormalities (transitional vertebrae, spina bifida occulta, increased/decreased lordosis, scoliosis) are found with equal incidence in symptomatic and asymptomatic individuals

- ? only an AP and lateral view are required; oblique and coned-down views offer little additional information

- indications for lumbo-sacral spine X-rays include:-

(* new-onset sciatica involving a single dermatome is not an indication for immediate lumbar spine X-rays because ~ 90% of cases are due to a herniated lumbar disc, which cannot be diagnosed by plain film X-rays => imaging studies can be deferred to the follow-up physician; multiple dermatome involvement suggests malignancy or infection or massive disc herniation and immediate imaging studies are indicated)

Bone scan

- moderate sensitivity for detecting spinal infection, tumor or occult fractures

- however, the specificity is low and a bone scan is probably best utilised as a screening test in a patient with a suspected occult fracture not visible on a plain film X-ray; or a bone scan + a sed rate can be used as a screening test in patients with suspected spinal metastasis or vertebral osteomyelitis

- no studies have compared the relative accuracy of a bone scan versus CT/MRI in the diagnosis of spinal infection or tumor or occult fractures

CT scan of the lumbar spine

- a CT scan's greatest utility is in fracture evaluation, or when vertebral osteomyelitis is suspected

- a CT scan is more useful than a MRI in defining bony details - especially the facet joints and posterior elements

- a standard CT scan cannot be used to exclude an epidural compression syndrome - unless it is used in conjunction with myelography; and a CT scan + myelography is indicated if a MRI is not available, or if a MRI is contra-indicated, or the patient is claustrophobic and/or cannot lie supine for prolonged periods

MRI of the lumbar spine

- a MRI provides the greatest degree of accurate anatomical detail - especially of the contents of the vertebral canal - compared to other radiological imaging studies

- an emergent MRI is immediately indicated if there any symptoms or signs of an epidural compression syndrome, or when a cancer patient presents to the ED with progressive neurological signs, or if there is a high clinical suspicion of an epidural abscess or an epidural hematoma

- an emergent MRI may be limited to the lumbo-sacral spine if an epidural compression syndrome due to a herniated lumbar disc is suspected, but the MRI study should include the entire spine if malignancy or infection or an epidural hematoma is suspected

- a non-emergent MRI may be indicated in the cancer patient, who presents to the ED with back pain + stable neurological signs, but the MRI can usually be delayed a few days and be performed as an outpatient study

- an emergent MRI is not indicated to investigate sciatica in the absence of significant (multi-dermatome) neurological deficits => defer MRI testing and refer the patient to the appropriate specialist, or consult a neurosurgeon in equivocal cases

- a MRI is contra-indicated in patients with pacemakers, intracardiac wires or mechanical heart valves, some intracranial aneurysm clips, or when metallic intraorbital foreign bodies are present

Blood tests

- blood tests are usually of no diagnostic utility

- an elevated WBC is a nonspecific test, and it has a low sensitivity for infection

- an elevated sed rate is rarely useful when used in isolation, because it a very non-specific test that has a variable sensitivity for infection or malignancy

- a sed rate should probably be ordered when historical factors, or examination findings, suggest spinal infection or malignancy => a positive test suggests that further spinal imaging or neuro-imaging studies may be warranted

(* a low sed rate should not be used to exclude spinal infection or malignancy if there is a strong clinical suspicion of disease)

 - a serum calcium should only be ordered when there is a strong clinical suspicion of hypercalcemia or malignancy

Post-void urinary catheterisation and urinalysis

- determination of the post-void urinary residual volume is usually only warranted if there is a strong clinical suspicion of urinary retention and overflow incontinence due to spinal cord or cauda equina pathology => a post-void residual volume of urine > 100 cc suggests neurogenic urinary retention and overflow incontinence (determined by catherization, or non-invasively by ultrasound)

(* a negative post-void large residual volume test virtually excludes a cauda equina syndrome with a > 99.9% negative predictive value)

- the presence of microscopic hematuria is not really useful because a significant minority of renal colic patients do not have hematuria, and microscopic hematuria may be an incidental finding in patients with an AAA or spinal disease

- pyuria could be secondary to pyelonephritis, but it could also merely represent the primary source of a secondary spinal infection (eg. vertebral osteomyelitis), which is actually causing the back pain

Medical decision making

- an EP should use a step-by-step algorithmic process to first consider (and exclude) life-threatening  or spinal cord-threatening pathology before considering (and excluding) less serious pathology

(* although the algorithmic process is described in a step-by-step manner, an EP should be thinking about all these steps simeultaneously when taking the history and examining the patient)

- the first step in the algorithmic process is to consider and exclude a distending/leaking/rupturing AAA in all patients > 60 years of age - especially if the patient has severe, intractable pain +/- associated abdominal pain +/- marked autonomic changes or hemodynamic instability

- clinical signs of a symptomatic AAA are highly unreliable, and a diagnostic workup is required if there is a high clinical suspicion of a symptomatic AAA

- an ultrasound is highly sensitive (~ 100%) in detecting the presence of an AAA, but it can rarely detect evidence of a leaking AAA or a small, contained retroperitoneal AAA rupture; an ultrasound also cannot assess the branch vessels or adequately evaluate the suprarenal aorta or thoracic aorta => an ultrasound is mainly used to screen patients at risk of an AAA

(* an ultrasound has the advantage that it can be readily performed at the bedside in an unstable patient, and it may also detect the presence of any free intra-peritoneal blood if an AAA has ruptured into the peritoneal cavity)

- a spiral CT scan of the abdomen should be ordered if there is a high clinical suspicion of a symptomatic AAA in a stable patient, because it can detect a subtle leaking aneurysm and it can also evaluate the status of the branch vessels

- the second algorithmic step (after considering the possibility of an AAA) is to consider the possibility of an epidural compression syndrome (due to tumor, infection, hematoma, or a massive disc herniation)

- an epidural compression syndrome should be suspected if the patient has definite neurological deficits suggestive of a cauda equina syndrome or a spinal cord syndrome

- it may be clinically possible to differentiate a lower spinal cord syndrome (conus medullaris syndrome) from a cauda equina sydrome - a spinal cord syndrome usually presents with early spastic bladder symptoms (urinary retention + spastic bladder spasms + secondary overflow incontinence) and the later development of motor deficits involving the large muscle groups of the lumbo-sacral area and proximal lower limbs (+/- flexor spasms and/or spastic paraplegic ataxia) + hyperreflexia + a positive Babinski response + sensory deficit below a certain dermatome level; while a cauda equina syndrome usually presents with lower motor neuron sensorimotor deficits specifically affecting the lower lumbar and sacral nerves (weakness of quadriceps, foot evertors, foot dorsiflexors, foot plantiflexors) + hyporeflexia + an absent Babinski response + flaccid-type bowel/urinary incontinence + absent anal sphincteric tone

(* it is not always possible, or even necessary, to clinically differentiate a spinal cord syndrome from a cauda equina syndrome - because emergency neuro-imaging is required in all patients with new-onset neurological deficits)

- all patients with a suspected epidural compression syndrome should have an emergent MRI (or CT scan + myelography) + dexamethasone IV (10 mg if suspected, and 100mg if definite) before performing the MRI study

- after considering, and excluding, the possibility of an epidural compression syndrome, the third algorithmic step is to consider the possibility of a spinal infection (vertebral osteomyelitis, discitis, epidural abscess)

- a spinal infection should be suspected if the following risk factors are present:-

(* fever is less likely to be present in patients with vertebral osteomyelitis than in patients with an epidural abscess; unexplained fever in a back pain patient is a "soft" physical sign because ~ 2% of back pain patients have a coincidental fever)

- a patient with a suspected spinal infection should have a CBC + sed rate + blood cultures (x 2) + radiological imaging study of the lumbo-sacral spine

(* plain film X-rays have a low sensitivity for infection and are only useful for vertebral osteomyelitis of > 6 - 8 weeks duration; plain film X-rays are not useful for diagnosing discitis or an epidural abscess => an emergent CT scan myelogram or MRI are the radiological imaging modalities of choice)

- after considering a spinal infection, the 4th algorithmic step is to consider the possibility of spinal malignancy (primary or secondary) involving the lumbo-sacral spine

- an underlying spinal malignancy should be suspected when the following risk factors are present:-

- there is no optimum approach to diagnosing a possible occult malignancy involving the lumbo-sacral spine - a plain film lumbo-sacral spine X-ray has a low sensitivity, but it is easy to order/perform in an ED setting; a CT scan (or MRI) has a higher sensitivity and higher specificity, but it does not necessarily have to be performed in the ED setting if there are no neurological signs, or other high-risk imperatives, present => it is appropriate to defer ordering a CT scan (or MRI) if the screening lumbar spine X-rays are negative => refer the patient to the primary care doctor (or appropriate specialist) for follow-up +/- further radiological imaging studies

- if a known cancer patient presents to the ED with back pain, immediate diagnostic studies are appropriate

- finally, in a patient with new-onset sciatica => consider neuro-imaging if the sciatica involves more than one dermatome (multi-dermatome sciatica), or if there are other "red flag" symptoms or signs suggesting serious pathology

- the presence of sciatica implies a herniated disc, but > 10 % of sciatica cases are due to other pathology - foraminal stenosis, piriformis syndrome, extraspinal plexus syndrome, spinal stenosis, compressive intraspinal tumor/infection - and further workup may be required if these other entities are suspected, or if the sciatica does not resolve within 6 weeks, or if the sciatica progressively worsens during the interim time period, or if multiple dermatome involvement becomes apparent over time

(* see the appendix for a detailed list of causes of non-discogenic sciatica)

- consult a neurosurgeon if there is a strong clinical suspicion (or any evidence) of an epidural compression syndrome, a spinal infection, a spinal malignancy or multi-dermatome sciatica

- if there is no evidence of a leaking AAA, or an epidural compression syndrome, or a spinal infection, or a malignancy involving the lumbo-sacral spine, or multi-dermatome sciatica, or intra-abdominal or pelvic pathology => treat the patient empirically with parenteral analgesics prn => po analgesics + outpatient follow-up (if the patient responds adequately to parenteral analgesics + patient can ambulate + home situation is compatible with the patient's degree of functional incapacity)

(* 90% of patients with acute lumbosacral strain have resolution of their symptoms in < 6 weeks => further diagnostic workup may be warranted if the back pain does not resolve within that time period)

Appendix

Sensory dermatomes

Motor testing

- there is no "pure" single nerve testing of the lower limbs

- some easy-to-remember combinations include:-

- the knee reflex is L 3/4 and the ankle reflex is S1

(* although many textbooks/journal articles suggest that first toe dorsiflexion innervation is primarily from L5, other textbooks/journal articles suggest S1 as the major innervation=> because of this discrepancy in opinions, it is recommended that you use foot and small toe(s) dorsiflexion for L5 testing and plantar flexion of the foot for S1 testing)

Grading of motor strength

Simplified screening evaluation of a patient with sciatica

Straight leg raising test

- this test is only used to determine whether a patient with back pain, who also has a history of pain that radiates down the lower limb to below the level of the knee, has a high likelihood of sciatica

(* > 80% of patients with a positive straight leg raising test have sciatica)

- the purpose of the test is to stretch the sciatic nerve by elevating the lower limb => stretches the inflammed/compressed sciatic nerve => induces pain in the lower leg or foot

(* increasing back pain, or buttock pain, or thigh pain is of no diagnostic relevance when performing the test - it is important to specifically ask the patient whether he develops any pain below the level of the knees)

- start off by having the patient lie supine with his pelvis flat on the bed and in a neutral position

- elevate the leg by cupping your hand below the patient's heel and slowly elevate the leg with the knee locked in extension => ask the patient whether elevating the leg causes any pain in the leg/foot below the ipsilateral knee

- a positive test = pain felt below the ipsilateral knee between 30 - 70° elevation

(* pain felt below < 30° elevation cannot be sciatica, because the sciatic nerve in not sufficiently stretched at that low elevation level)

- if pain is felt below the knee in the opposite (symptomatic) leg while the ipsilateral (asymptomatic) leg is being raised => highly specific for sciatica of the opposite leg (crossed straight leg raising test) - although it is a very insensitive test

- the accuracy of the straight leg raising test can be enhanced by the following maneuvers:-

- an alternative method of performing the straight leg raising test is to perform the sitting knee extension test
=> with the patient sitting on the edge of the table/stretcher with both hips and knees flexed to 90° => slowly straighten the one leg as if to evaluate the foot => patient adjusts posture by falling back (positive flip sign) => a positive test has the same significance as the supine straight leg raising test

(* the straight leg raising is not a full-proof test for sciatica and there are other causes of a positive straight leg raising test - myogenic pain syndromes, tight hamstrings or injured calf muscles)

Non-discogenic causes of sciatica

Hip or gluteal region

Thigh region Hip or thigh region Wadell's criteria

- these criteria are used to evaluate a patient with probable non-organic back pain

- the more criteria that are present => the greater the likelihood that the back pain could be non-organic; and > 3 criteriae should suggest non-organic pathology

Tenderness

Pain responses to simulation maneuvers Distraction maneuvers Regional disturbance Over-reaction
Differential diagnosis of back pain in ED patients
 Immediate threat to life
  • AAA
  • pulmonary embolism
  • aortic dissection
  • acute myocardial infarction
 Immediate threat to spinal cord
  • epidural hematoma
  • epidural abscess
  • epidural tumor
  • massive disc herniation
 Urgent threat

 Cardiac

  • endocarditis
 Renal
  • pyelonephritis
  • perinephric abscess
  • renal colic
  • renal artery embolus or dissection
 Abdominal and visceral
  • perforated gastric ulcer
  • pancreatitis
  • acute cholecystitis
  • retroperitoneal hematoma or abscess
  • prostatitis
 Gynecological 
  • ectopic pregnancy
  • pelvic infection
  • endometriosis
  • ovarian pathology
 Vertebral
  • unstable fracture
  • osteomyelitis
  • Pott's disease (TB of the spine)
  • Tumor 
  • herniated disc
  • discitis
 Less urgent threat
  • lumbosacral strain
  • degenerative processes of spine and discs and facet joints
  • spinal stenosis
  • osteoporosis with compression fracture
  • congenital kyphosis/scoliosis
  • spondylolithesis
  • inflammatory arthritis (ankylosing spondylitis, psoriatic arthritis, rheumatoid arthritis, Reiters syndrome, arthritis associated with inflammatory bowel disease)
  • Scheurmann's disease (osteochondritis)
  • Shingles
  • Paget's disease

 
Clinical clue table
Clinical clues Suggests
Age < 10 years Discitis, tumor, tuberculous vertebral osteomyelitis, bacterial osteomyelitis, congenital disorders
Age 10 - 18 years Spondylolysis, spondylolisthesis, Scheurmann's disease, oversue syndrome, tumor, herniated disc, vertebral osteomyelitis, ankylosing spondylitis
Age > 50 years Malignancy, spinal stenosis, AAA
Pain worse with movement and certain postures; pain relieved by rest Musculoskeletal - mechanical
Pain worse with coughing, sneezing, straining at stool or in moving car Herniated disc
Pain worse at rest, or pain worse at night awakening patient from sleep, or unrelenting pain, or pain lasting > 6 weeks Spinal infection or malignancy
Pain worse with walking, especially in hyperextension and relieved by stooping or flexed posture Spinal stenosis
Pain radiates to below the knee Sciatica
Pain radiates to anterolateral thigh and anterior knee L4 nerve root compression syndrome
Pain radiates to posterolateral thigh, lateral calf, dorsum of foot, medial toes; difficulty walking on heels L5 nerve root compression syndrome
Pain radiates to posterior thigh, calf, heel, sole of foot, lateral toes; difficulty walking on toes S1 nerve root compression
Pain worse in the am, pain improves during the day and with activity +/- morning stiffness Ankylosing spondylitis or other inflammatory arthritis
Back pain radiating to the abdomen AAA, renal colic, primary intra-abdominal pathology
Abdominal pain radiating to the back  AAA, perforating PUD, cholecystitis, pancreatitis, renal colic
Pain localised to the mid-upper back Spinal hematoma, aortic dissection, AMI, pulmonary embolism
Pain localised to one side of back Shingles, unilateral paraspinal pathology, referred pain from abdominal or retro-peritoneal pathology
Weight loss Malignancy, underlying immunocompromised state, tuberculosis
Fever, chills, night sweats Spinal infection, spinal malignancy, acute transverse myelitis, bacterial endocarditis, inflammatory arthritis, connective tissue disease, referred back pain from retro-peritoneal or abdominal inflammatory pathology
Genito-urinary symptoms Renal colic, pyelonephritis, peri-nephric abscess, prostatitis, early spinal cord compression syndrome
Altered bowel habits Rectal malignancy, cauda equina or spinal cord syndrome, inflammatory bowel disease disease
Vaginal discharge, pelvic pain Pelvic infection, secondary spinal infection
History of conjunctivitis Reiters syndrome
History of uveitis Ankylosing spondylitis, rheumatoid arthritis
IV drug abuse Epidural abscess, vertebral osteomyelitis, endocarditis
Alcohol abuse Epidural abscess, pancreatitis, perforating PUD
Chronic corticosteroid use Immunosuppression, occult vertebral fractures
Anticoagulants or bleeding diathesis Epidural or retroperitoneal hematoma
Osteoporosis Occult vertebral compression fractures
History of trauma Vertebral fracture, herniated disc, back strain 
History of known malignancy Vertebral metastasis, epidural metastasis, metastatic plexus lesions, carcinomatous meningitis, paravertebral tumor masses
Recent penetrating trauma, LP or back surgery Spinal infection
Hypotension and/or syncope AAA, ectopic pregnancy, sepsis
Restless, writhing patient Colic - renal, biliary, ovarian torsion
Skin rash Psoriatic arthropathy, endocarditis, connective tissue disease
Skin cellulitis, skin popping Spinal infection
Palpable tenderness of spine Spinal infection, spinal malignancy
Limited ROM of spine Musculoskeletal spine - non-specific
Limited ROM of hip Referred pain from hip pathology, or back pain secondary to pelvic tilt
Tenderness over sacrum or sacro-iliac joints Sacro-ileitis
Tenderness over ischial tuberosity Ischiotuberal bursitis
Unilateral neurologic deficit Sciatica
Bilateral neurologic deficit Epidural compression syndrome

Disclaimer: My EM guidemaps reflect my personal approach to problem-solving/managing clinical cases in an ED setting and they should not be regarded as the standard of care. They merely represent the personal opinions of the author and they should only be used in clinical practice if the reader-user has substantial reason to believe that the clinical advice contained in the guidemaps is valid and accurate. The guidemaps are not meant to be "authoritative" and the reader-user should consult standard medical textbooks and expert opinion articles/guidelines for more authoritative advice. The reader-user should particularly confirm all drug doses, their indications and contra-indications, prior to their use.