Sensory dermatomal representation in the medial lemniscus.

BACKGROUND Restricted sensory deficits along the somatotopic topography of the medial lemniscus rarely develop in medial medullary infarction. We describe a patient with medial medullary infarction who presented with dermatomal sensory deficits caused by a medial lemniscal lesion. CASE DESCRIPTION A 58-year-old man presented with sudden right-sided hemiparesis and paresthesia. He had noticed the paresthesia below the level of the right L5 dermatome, where his vibration and position senses were mildly diminished. His paresthesia was more severe over the right calf and foot. Magnetic resonance images of the brain showed an acute small infarct in the medial-ventral portion of the left rostral medulla oblongata. A nerve conduction study and electromyography showed no abnormalities. At follow-up, the patient's motor and sensory deficits had improved considerably. CONCLUSIONS The patient showed lemniscal sensory deficits below the right L5 dermatome that were caused by the partial involvement of the medial lemniscus. These findings suggest that lemniscal sensory dermatomal representation is preserved at least up to the level of the medulla oblongata.