1619 - Tibial nerve compression by calf mass mimicking lumbar radiculopathy: a case report

We describe a male with concerns of cervical myelopathy ultimately traced to tibial nerve compression by an occult mass.

Case Description:

A 55-year-old male with history of rheumatoid arthritis and prior cervical decompression presented with right plantar hypoesthesia and pain radiating in the L5-S1 distribution following right knee arthrocentesis. Examination showed upper motor neuron signs but a focal plantar sensory deficit and selective toe-flexor weakness, with preserved dorsiflexion and toe extension. Cervical MRI demonstrated multilevel spondylosis and focal myelomalacia; lumbar MRI showed degenerative changes deemed distinct from the patient’s presenting pathology. Electrodiagnostic testing revealed an acute, axonal tibial mononeuropathy on the right lower extremity without myotomal evidence of lumbosacral radiculopathy. A follow up targeted lower limb MRI identified a 6×3×20 cm lobulated T2-hyperintense lesion between the soleus and medial gastrocnemius producing mass effect on the tibial nerve. Contrast MRI was ordered, and surgical/oncologic consultation were expedited.

Discussions:

Plantar numbness with toe-flexor weakness is often attributed to polyneuropathy or lumbosacral radiculopathy, particularly in patients with coexisting cervical or lumbar disease. Differential should remain open beyond polyneuropathy and radiculopathy to include tibial mononeuropathy, particularly tarsal tunnel or proximal tibial lesions. In this case, electrodiagnostics localized the lesion to the tibial nerve, decisively redirecting imaging from the spine to the symptomatic limb, where MRI revealed an occult compression.

Conclusions:

Coexisting cord pathology can distract from a distal, focal process. Differential for plantar numbness with accompanied loss of toe flexion should include consideration for tibial mononeuropathy.