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Approach to focal weakness

The same eight steps, every presentation: threats first, then the history and exam that discriminate, one honest sentence, a mechanism-grouped differential, and the tests read in order.

  1. Immediate threats

    • Sudden focal deficit is a stroke code: time of onset (or last seen well) decides therapy eligibility
    • Glucose first: hypoglycemia is the great stroke mimic and the fastest fix in medicine
    • Airway and swallow before anything passes the lips
    • Back pain with bilateral leg weakness, saddle anesthesia, or retention: cord compression or cauda equina, image the spine urgently

  2. History that discriminates

    • Exact onset and evolution: maximal at onset (vascular) versus marching over minutes (seizure, migraine) versus days (inflammatory, compressive)
    • Distribution the patient describes: face-arm-leg on one side, both legs, one limb, or patchy
    • Negative versus positive symptoms: loss of function points vascular; tingling and jerking point elsewhere
    • Anticoagulants, recent trauma, cancer history, immunosuppression

  3. Examination

    • The pattern is the localizer: upper motor signs (spastic, brisk, upgoing) versus lower (flaccid, wasted, absent)
    • Face involvement and its sparing pattern; visual fields; neglect and language
    • A sensory level on the trunk places the lesion in the cord
    • Pulses and rhythm: AF found now changes the rest of the workup

  4. Problem representation

    A 74-year-old in AF, off anticoagulation, with sudden right face-and-arm weakness and aphasia maximal at onset (points at left MCA stroke) versus a 30-year-old with two days of ascending bilateral leg weakness and absent reflexes after gastroenteritis (points at Guillain-Barre).

  5. Differential, by mechanism

    Vascular

    • Ischemic stroke
    • Hemorrhage
    • TIA

    Compressive

    • Cord compression
    • Cauda equina
    • Peripheral entrapment

    Inflammatory / demyelinating

    • Guillain-Barre
    • Multiple sclerosis
    • Transverse myelitis

    Mimics

    • Hypoglycemia
    • Todd's paresis
    • Hemiplegic migraine
    • Functional weakness

  6. Investigations

    • Bedside glucose before the scanner
    • Non-contrast CT head immediately: its first job is excluding hemorrhage, not proving infarct
    • ECG for the AF that explains it; swallow screen before oral intake
    • Urgent MRI whole spine when the level or the story says cord
    • Nerve conduction and LP where the peripheral pattern says Guillain-Barre (protein up, cells near-normal)

  7. Interpretation

    • Upper versus lower motor neuron is the first branch; everything downstream depends on it
    • A normal early CT plus a persisting deficit is still a stroke: treat the clinic, not the pixel
    • Reflexes falling with rising weakness after an infection reads as Guillain-Barre; watch the vital capacity, not just the legs

  8. Next steps

    • Stroke pathway activation within the window; aspirin after hemorrhage is excluded when outside it
    • Dexamethasone and urgent oncology/surgical referral for malignant cord compression
    • Guillain-Barre earns monitored beds: serial spirometry, cardiac monitoring, and immunoglobulin or exchange

Connected

TopicLocalize before you listApproachWhen weakness comes with confusionECGThe rhythm that explains it

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