What is the appropriate diagnosis and first‑line management for a patient with chronic plantar fasciitis causing compression of the distal tibial and common peroneal (fibular) nerves resulting in a left‑leg mononeuropathy?

Diagnosis and Management of Nerve Compression from Plantar Fasciitis

Primary Recommendation

This clinical presentation requires immediate reassessment because plantar fasciitis does not cause tibial-peroneal nerve damage or mononeuropathy—these are separate conditions requiring distinct diagnostic workup and management. The described nerve damage is not a recognized complication of plantar fasciitis and suggests either misdiagnosis or concurrent pathology requiring urgent evaluation.

Diagnostic Clarification

Why This Presentation Doesn't Fit Plantar Fasciitis

• Plantar fasciitis is a degenerative condition of the plantar fascia at its calcaneal origin, not a compressive neuropathy 1, 2
• Typical symptoms are stabbing, non-radiating heel pain worse with first morning steps and at day's end, with tenderness at the anteromedial calcaneus 3
• Nerve damage and mononeuropathy are not features of plantar fasciitis and indicate alternative or additional diagnoses 1, 3

Alternative Diagnoses to Consider

The combination of distal tibial and common peroneal nerve involvement below the knee suggests:

• Tarsal tunnel syndrome (tibial nerve compression at the medial ankle) should be considered as it can present with similar location of symptoms 4
• Common peroneal nerve entrapment at the fibular head or more distally
• Compartment syndrome if there is history of trauma or acute onset
• Peripheral neuropathy from systemic causes (diabetes, vasculitis, inflammatory conditions) 5

Required Diagnostic Workup

Electrodiagnostic Studies

• Nerve conduction studies and EMG are essential to confirm mononeuropathy, localize the lesion, and assess severity 5
• These studies can differentiate between focal nerve compression versus polyneuropathy 5

Imaging Studies

• Weightbearing radiographs should be obtained initially (85% sensitivity, 95% specificity) to exclude fractures, bone pathology, or other structural abnormalities 4, 6
• MRI is the most sensitive imaging modality for evaluating both soft tissue pathology and nerve compression, and should be obtained when diagnosis remains uncertain 4, 6
• Ultrasound can assess plantar fascia thickness (>4mm is abnormal) and evaluate for masses or fluid collections compressing nerves 4, 6

Specialized Testing if Indicated

• Skin biopsy with intraepidermal nerve fiber density may be considered if small fiber neuropathy is suspected, though specificity is limited (45-90% sensitivity, 95-97% specificity) 5
• Nerve biopsy is reserved for suspected vasculitis, infiltrative disorders, or inflammatory neuropathies when less invasive testing is inconclusive 5

Management Algorithm

Immediate Steps

1. Refer for urgent electrodiagnostic evaluation to confirm and localize nerve pathology 5
2. Obtain MRI of the foot, ankle, and lower leg to identify structural causes of nerve compression 4, 6
3. Screen for systemic causes: diabetes, inflammatory conditions, vasculitis, vitamin deficiencies 5

If Plantar Fasciitis is Confirmed Concurrently

• Initial conservative treatment: stretching of plantar fascia, ice massage, NSAIDs, and activity modification 3
• Physical therapy with specific stretching techniques for the plantar fascia and Achilles tendon 1, 3
• Avoid corticosteroid injections initially as evidence increasingly favors alternatives like platelet-rich plasma or dextrose prolotherapy 7
• 80-90% of patients improve with conservative treatment within 12 months 1, 2, 3

If Nerve Compression is Confirmed

• Management depends entirely on the specific nerve(s) involved and the underlying cause identified on imaging and electrodiagnostic studies
• Surgical consultation may be required for decompression if structural compression is identified
• Treatment of underlying systemic conditions if present

Critical Pitfalls to Avoid

• Do not attribute neurologic deficits to plantar fasciitis alone—this delays appropriate diagnosis and treatment of the actual nerve pathology 1, 3
• Do not proceed with plantar fascia-directed treatments (injections, shock wave therapy, fasciotomy) without first establishing the correct diagnosis for the neuropathy 7, 3
• Correlation of imaging findings with clinical symptoms is essential—some MRI findings can be present in asymptomatic patients 6
• Absence of fever or systemic symptoms does not exclude serious pathology requiring urgent intervention 5