Natural course

The vast majority of low back pain cases presenting to the general practitioner have a benign cause, evolution and outcome. Up to 70% of them are classified as nonspecific strains or sprains, and remission occurs within 2 weeks in 90% of those presenting with acute episodes. Low back pain tends to become chronic or recurrent in some patients, associated with depressive mood or symptoms, but even the majority of such cases have a good functional outcome. It's important, therefore, that patients are fully informed on the probable cause at the first acute episode, and reminded of it later, if and when recurrences occur.

The pain of a herniated disk shows slower improvement than that of a sprain; about 10% require surgery for persistent pain lasting 6 weeks or more. Objective evidence for non-surgical regression of herniated disk within 6 months in two thirds of cases has been established by sensitive imaging technique. In contrast, spinal stenosis remains stable in 70% of cases, but progression is reported in 15%, and 15% show regression. Return to work after an acute episode is influenced by both socio-economic and clinical factors, and will be the subject of another article. Low back pain is rarely disabling.

The diagnostic challenge

The most important step in the diagnostic challenge is to detect an underlying treatable cause and then initiate its management.

First, low back pain is occasionally a symptom of diseases that are unrelated to the musculoskeletal apparatus of the lumbar spine and is, therefore, non-mechanical in essence. Such diseases may involve pelvic (prostate, ovaries, uterus) or retro-peritoneal organs (kidney, aortic aneurysm, pancreas, gallbladder, perforated gastro-duodenal ulcer); they account for only 2% of the low back pain cases seen in general practice, but they should always be considered when taking the history and assessing various risk factors.

Second, major underlying diseases involving the musculoskeletal lumbar system should be considered; they are of 3 types and relatively rare (1%) in general practice: neoplastic (multiple myeloma, metastatic carcinoma, spinal cord tumors), metabolic (osteopenia, Paget's disease of bone, etc.) and inflammatory (i.e. HLA-B27 associated diseases). Infections such as osteomyelitis, septic diskitis, etc. are extremely rare.

Third, mechanical low back or leg pain account for 97% of all consultations. The most frequent (70%) are idiopathic - nonspecific conditions without an obvious cause - often termed sprains or strains. These are presumed mechanical lesions affecting the muscles and ligaments of the lumbar spine, but direct evidence of a lesion is absent in most of these cases. Age-related degeneration (osteoarthritis) affects disks and articular facets, accounting for approximately 10% of cases. Herniated disk, spinal stenosis and osteoporotic compression fracture together account for about 4% of cases, but compression fracture frequency is higher in practices that have a high proportion of elderly. Spondylolisthesis and internal disk disruption (or diskogenic low back pain) are less frequently observed as causes of back pain. Congenital disease (scoliosis, kyphosis) is also a rare cause. It should be noted that many people with spondylolysis have no pain.

The history

A careful history should reveal if there is pain at night as well as other circumstances of pain occurrence. These can be important indicators, but they are unfortunately rather non-specific and not always sensitive for any of the major categories cited above. The presence of sciatica and leg numbness or pain exacerbated by cough, sneezing or the Valsalva maneuver all indicate neurological involvement, for which a culprit lesion must be identified if symptoms persist for more than 2 or 3 weeks. The existence of claudication-type symptoms (pseudo-claudication) or numbness in the legs that is relieved by spinal flexion or aggravated by extension requires a search for spinal stenosis, especially after the age of 60.

The clinical examination

Results of the physical examination of lumbar flexibility, range of motion and vertebral tenderness are not very specific. Ipsilateral straight-leg-raising of less than 60 degrees with pain radiating below the knee is sensitive in revealing nerve root compression, but this test may be normal in spinal stenosis and thus also lacks specificity. By contrast, crossed straight-leg-test raising with symptoms produced in the opposite leg is highly specific for nerve root compression but it's not a sensitive test. Dorsiflexion strength of the big toe and ankle examine the integrity of L5, while plantar flexion and the ankle jerk reflex test for S1. The knee reflex may be absent in L4 involvement. Only 5% of cases of sciatica involve roots other than L5-S1.

Imaging exams: standard X-ray, Computerized Tomography (CT) and Magnetic Resonance Imaging (MRI)

Indications for imaging studies in patients with low back pain include: a history of fever, loss of body weight, a history of cancer or trauma, neurological deficits, alcohol or injection-drug abuse, and age above 50. However, strict adherence to these guidelines can lead to overuse and sound medical judgment is needed. Knowledge of the patient's history and the natural course of the episode usually provide useful guidance as to when to perform CT or MRI.

CT and MRI are more sensitive than conventional radiology in detecting spinal infection, cancer, a herniated disk and spinal stenosis. Compression (osteoporotic) fractures and spinal stenosis occur more frequently after the age of 60. Therefore the authors recommend that the more sensitive imaging techniques are selected for those patients with suspicion of cancer, infection or persistent neurological signs and symptoms beyond 3 to 6 weeks, or for those elderly at risk of osteoporotic complications or with symptoms suggestive of spinal stenosis.

Close to 40% of asymptomatic adults over 60 have one of the following abnormalities on MRI: a herniated disk, a bulging disk, a degenerative disk, spinal stenosis or an annular tear. Therefore, CT or MRI detection of lesions affecting the major anatomical components of the lumbar spine requires skilful interpretation, as their presence does not necessarily establish a causal relationship with back pain, and their correction may not result in clinically meaningful relief.

Electromyography or somato-sensory evoked potentials can help to define the extent of any neurological involvement and to differentiate root compression syndrome from peripheral neuropathy. In most cases, however, CT and MRI are the standard diagnostic tests. Nowadays, myelography is used much less frequently than before, but it is still performed pre-operatively in selected cases.

A future article in this series will discuss the treatment options for low back pain.