What are the possible causes of recurrent morning foot drop that resolves within 24 hours in an adult?

Recurrent Morning Foot Drop Resolving Within 24 Hours

The most likely cause of recurrent foot drop occurring specifically upon waking and resolving within 24 hours is compression of the common peroneal nerve at the fibular head during sleep, typically from habitual leg positioning or leg crossing during the night. 1, 2

Primary Diagnostic Considerations

Common Peroneal Nerve Compression (Most Likely)

• Habitual leg crossing or specific sleep positioning is the most frequent reversible cause of peroneal neuropathy, and most patients improve when they stop this habit 1
• The common peroneal nerve is most vulnerable to compression at the fibular neck where it wraps around the bony prominence of the fibula 1, 2
• Morning-specific symptoms that resolve within hours strongly suggest positional compression during sleep rather than structural nerve damage 2
• The superficial location of the nerve at the fibular head makes it susceptible to external compression from leg-on-leg positioning, tight bedding, or sleeping against hard surfaces 2

Less Common but Important Causes

• Lumbar L5 radiculopathy can present with foot drop but typically causes persistent symptoms rather than transient morning-only weakness 1, 3
• Sciatic nerve compression at the sciatic notch may occur from prolonged hip flexion during sleep but usually presents with additional posterior thigh symptoms 3
• Anterior horn cell disease would not explain the recurrent, self-resolving pattern 1
• Cortical infarction can rarely cause isolated foot drop but presents acutely rather than recurrently, and would not spontaneously resolve within hours 4

Essential Clinical Evaluation

Neurological Examination Specifics

• Test dorsiflexion strength (tibialis anterior) and foot eversion (peroneal muscles) to confirm the distribution of weakness 1, 2
• Assess sensation over the dorsum of the foot and lateral lower leg, as sensory loss in this distribution confirms peroneal nerve involvement 2
• Examine for foot inversion weakness, which would suggest L5 radiculopathy or sciatic nerve involvement rather than isolated peroneal neuropathy 1, 3
• Check for symmetry of symptoms, as painful diabetic peripheral neuropathy is invariably symmetrical, so unilateral symptoms should prompt evaluation for compressive causes 5

Gait and Functional Assessment

• Observe for steppage gait (high-stepping to clear the dropped foot), which is characteristic of peroneal nerve dysfunction 2
• Document whether the patient can walk on their heels, as inability indicates weakness of ankle dorsiflexors 1

Provocative Testing

• Palpate the fibular head for tenderness or masses that might compress the nerve 2
• Assess for Tinel's sign at the fibular neck by tapping over the nerve to reproduce symptoms 2

Diagnostic Studies

Electrodiagnostic Testing

• Nerve conduction studies and electromyography are useful adjuncts in localizing the site of injury, establishing the degree of damage, and predicting recovery 1
• Motor nerve conduction studies can demonstrate slowing across the fibular head in cases of compression 2
• EMG findings help differentiate between nerve compression, radiculopathy, and anterior horn cell disease 1
• For recurrent transient symptoms, testing should ideally be performed during or immediately after an episode when possible 2

Imaging Considerations

• MRI of the knee can identify structural causes of peroneal nerve compression including masses, ganglion cysts, or fibular head abnormalities 1, 2
• Lumbar spine MRI is indicated if examination suggests L5 radiculopathy rather than isolated peroneal neuropathy 1, 3
• Ultrasonography can visualize the peroneal nerve at the fibular head and identify compression or nerve swelling 1

Management Approach

Conservative Management (First-Line)

• Instruct the patient to avoid leg crossing and identify/modify sleep positions that may compress the nerve 1, 2
• Recommend avoiding external compression from tight bedding, knee-high socks, or boots 2
• Provide ankle-foot orthosis (AFO) if symptoms persist or worsen to enable safer walking and prevent equinovarus contracture 1, 3
• Reduce inflammation with activity modification and potentially anti-inflammatory medications 2

Surgical Intervention

• Microsurgical decompression at the fibular tunnel is indicated when symptoms are refractory to conservative management for 3-6 months 2
• Fibular head dysfunction causing nerve compression may respond to osteopathic manipulative treatment in select cases 6
• Surgical options should be considered before permanent nerve damage occurs 2

Critical Pitfalls

• Do not assume all foot drop is benign positional compression—progressive or persistent symptoms require urgent evaluation for stroke, particularly in patients with vascular risk factors 4
• Avoid delaying electrodiagnostic studies in cases where symptoms are becoming more frequent or prolonged, as this may indicate progressive nerve damage 1, 2
• Peripheral neuropathy from diabetes may completely mask pain, delaying recognition of developing nerve compression 5
• Do not overlook lumbar spine pathology in patients with additional symptoms such as back pain, radicular pain, or bowel/bladder dysfunction 1, 3