In an adult patient, which disease can cause recurrent foot drop episodes lasting less than 24 hours up to six weeks?

Recurrent Transient Foot Drop: Multiple Sclerosis as Primary Consideration

Multiple sclerosis (MS) is the most likely disease causing recurrent foot drop episodes lasting less than 24 hours to 6 weeks, as these represent classic MS relapses (attacks) that by definition last at least 24 hours and typically reach maximum disability within 2-4 weeks. 1

Understanding MS Attacks and Foot Drop

An MS "attack" (relapse/exacerbation) must last at least 24 hours by diagnostic criteria, with separate attacks defined as events separated by at least 30 days from onset to onset. 1 This timing precisely matches your clinical scenario of recurrent episodes lasting less than 24 hours up to 6 weeks.

Key Clinical Features Supporting MS Diagnosis

• Motor weakness in MS typically starts distally and can present as isolated foot drop, even mimicking peripheral nerve lesions with lower motor neuron findings on examination. 2, 3
• MS can masquerade as a peripheral process, presenting with painless foot drop and lower motor neuron findings despite being a central demyelinating disease. 2
• Reflexes may be decreased or absent initially, though upper motor neuron signs eventually emerge in most cases. 1

Diagnostic Approach

MRI is the most sensitive and specific test for MS diagnosis, requiring at least 3 of 4 Barkhof criteria: (1) one gadolinium-enhancing lesion or nine T2 hyperintense lesions; (2) at least one infratentorial lesion; (3) at least one juxtacortical lesion; (4) at least three periventricular lesions. 1

Apply the 2017 McDonald Criteria combining clinical presentation, neurologic examination, and MRI findings to establish dissemination in space and time. 1, 4

Critical Differential Diagnosis Pitfall

In MS patients with acute foot drop, always perform detailed neurophysiological studies to exclude peroneal nerve compression at the fibular head, which can occur from leg crossing or wheelchair positioning in patients compensating for MS-related ataxia. 3 This is particularly important because:

• Six of ten MS patients with acute foot drop in one series had peripheral peroneal nerve compression rather than a new MS attack. 3
• Only detailed neurophysiological examination distinguished peripheral compression from central demyelination. 3
• Avoiding the causative posture (hard leg crossing, genu recurvatum to compensate for ataxia) led to clinical improvement in 5 of 7 patients. 3

Alternative Diagnoses to Consider

Guillain-Barré Syndrome (Less Likely)

GBS typically presents with rapidly progressive bilateral weakness reaching maximum disability within 2 weeks (rarely up to 4 weeks), making the 6-week duration and recurrent pattern atypical. 1

• GBS has a monophasic clinical course; recurrence is rare (2-5%), distinguishing it from your recurrent presentation. 1
• Treatment-related fluctuations occur in only 6-10% of GBS patients within 2 months of initial improvement. 5

Other Considerations

Conus medullaris syndrome can cause lower limb motor disturbances but typically presents with prominent early bladder/bowel dysfunction and does not follow a relapsing-remitting pattern. 6

Management Implications

For confirmed MS relapses causing significant functional impairment, initiate intravenous methylprednisolone (typically 1000 mg daily for 3-5 days) as the mainstay of acute treatment. 4

Patients who do not adequately respond to steroids may benefit from plasma exchange or intravenous immunoglobulin. 4

Disease-modifying therapy should be initiated to slow disease progression and reduce relapse frequency, with options including injectable agents, infusions, and oral medications. 4

Prognosis and Monitoring

Recovery from MS relapses can continue for more than 3 years after onset, though most improvement occurs within the first few months. 1

Relapses carry a relatively high risk of incomplete remission resulting in residual disability, emphasizing the importance of early diagnosis and treatment. 7

Approximately 80% of patients with MS maintain walking ability, though functional electrical stimulation may be needed for persistent foot drop to reduce fall risk and improve gait efficiency. 5, 8