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This case illustrates an unusual cause of calf hypertrophy. A 47 year old man presented with a two year history of progressive swelling of the right calf. Initially painless, he later developed a dull ache over the lateral aspect of the lower leg. There was no weakness, nor any family history of muscle disease. On examination the right calf was enlarged, the right ankle reflex was absent and there was a S1 dermatomal sensory loss to pinprick. Investigations revealed a normal creatinine kinase; an enlarged soleus with altered signal on MRI of the calf; and features of active denervation on a calf muscle biopsy. MRI of the lumbosacral spine demonstrated the cause: a right lateral disc prolapse at L5/S1 causing a S1 radiculopathy. Nerve conduction studies were normal; electromyography of right gastrocnemius showed fibrillation potentials, positive sharp waves, and sparse isolated spontaneous muscle potentials but no neuromyotonia.
Calf hypertrophy in sciatica was noted as early as 1848 by Robert Graves1 and subsequently by Lhermitte2 in 1918. Since then neurogenic muscle hypertrophy has been reported in traumatic peripheral nerve lesions, polyneuropathies, spinal muscular atrophy, and S1 radiculopathies. Suggested mechanisms have included a response to increased work in the remaining intact muscle fibres, increased stretch of muscle fibres by antagonist muscles, and neuromyotonia.3