[HTLV-I associated myelopathy presenting with profound atrophy of unilateral lower limb].

A 63-year-old woman had suffered from progressive weakness and wasting of the right lower limb for seven years. In the lower limbs, there were profound muscular atrophy and weakness on the right, and mild weakness with spasticity on the left. Muscle strength of the upper limbs was normal. Sensory examination was normal except for paresthesias below the right knee. Anti-HTLV-I antibody titer was raised both in serum and in the CSF. Motor nerve conduction studies of the lower limbs showed small compound muscle action potentials and somewhat slow conduction velocities, more evident in the right side. F-wave was evoked only in the left tibial nerve and its latency was increased. Sensory nerve conduction studies were normal in the lower limbs. Somatosensory evoked potentials (SEPs) after tibial nerve stimulation at the ankles showed increased interpeak latencies between lumbar N20 and scalp P37. Nerve conduction studies in the upper limb were normal. Single fiber electromyography suggested anterior horn involvement not only in the lumbosacral cord but also in the cervical cord. Weakness and spasticity improved after oral administration of prednisolone. The SEPs findings and a favorable response to prednisolone excluded the possibility of amyotrophic lateral sclerosis. This case is a clinical variant of HTLV-I-associated myelopathy presenting profound atrophy of unilateral lower limb.