Differential diagnosis

Process of comparing possible causes of a set of symptoms and clinical findings.

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Comparing plausible explanations

Differential diagnosis is the process of comparing possible causes of a symptom. For leg pain, possibilities may include a lumbar root, hip joint, peripheral nerve, vascular disorder or several coexisting problems. It does not mean assigning the symptom to the first abnormality visible on an image.

The history explores onset, distribution, triggers and associated findings. Examination then seeks observations that strengthen or weaken each hypothesis. Investigations should address useful uncertainty rather than search for every possible abnormality. A working diagnosis may change over time. Failure to respond to treatment is a reason to reconsider the explanation instead of indefinitely repeating the same strategy. The patient can contribute by describing changes clearly, including new symptoms outside the original painful region.

Interpret a finding in context

A clinical finding increases or decreases the plausibility of a diagnosis; it does not replace the full assessment. The clinician compares it with the history, strength, sensation and other relevant observations. An isolated response can be affected by pain, positioning, apprehension or normal variation. Comparison between sides and, when appropriate, between visits is often more informative than a single number. A finding becomes useful when it helps answer a specific clinical question rather than simply adding a label.

How it changes care

The result may lead to activity modification, another investigation, medical referral or continued conservative management. One test should not determine the choice of a therapeutic machine. At TAGMED, findings should help establish a working explanation and measurable goals, followed by review of response to care. Worsening strength or walking requires reassessment. Recent urinary changes or loss of perineal sensation requires emergency evaluation even when another test seems reassuring. Examination also identifies situations in which routine treatment should be postponed. The patient should leave understanding what the finding means, what remains uncertain and what change would require an earlier review.

Frequently asked questions

Does changing a hypothesis make assessment pointless?

No. Reassessment is part of careful clinical reasoning as new information becomes available.

Does a positive test establish a diagnosis?

No; it must be considered alongside the other assessment findings.

Does a normal result rule out every disease?

No. Each test addresses particular functions or diagnostic possibilities.

Must it be repeated at every appointment?

Only when repetition adds useful information for decisions or monitoring.

Does the result select a treatment?

No. Diagnosis, safety, preferences and practical goals remain essential.

Educational information from The Spine Page. This entry does not replace an individual assessment. Documentary version: October 12, 2026. Sylvain Desforges, B.Sc., D.O., N.D., osteopath and naturopath.