A Man With Weakness in the Legs

A 36-year-old patient was referred for evaluation of progressive weakness in the legs and feet numbness for 4 years.

Past medical history and family history were noncontributory. He did not smoke or drink.

Examination revealed normal mentation and cranial nerves. He was able to walk on his heels and toes. Muscle strength was 5/5 in the neck, and arms proximally, 4/5 in the hand muscles; hip flexion, extension, and adduction were 4/5; leg flexion and extension were 5−/5; the foot extensors, dorsiflexors, and evertors were 3/5; flexors were 4/5. Reflexes were trace at the knees and triceps and absent elsewhere. Toes were down-going. There was absent vibration sense in the toes and decreased in the ankles and fingers. Position sense was decreased in the toes. He had decreased pinprick, touch, and temperature sensations to 16 cm above both ankles and up to the wrists in the upper extremities. Romberg test and gait were normal. The rest of the neurologic examination was normal, and there was no visceromegaly, nerve hypertrophy, or high arches. No muscle atrophy was noted.

What is the Differential Diagnosis?

This patient, with a negative family history, developed a polyneuropathy with proximal and distal weakness, areflexia, and prominent sensory loss of large fibers, but also small fibers (decreased pain and temperature sensations). Common causes of polyneuropathies to be considered include diabetes, thyroid disease, toxins, HIV infections, monoclonal gammopathy, and B ₁₂ deficiency. He was not an alcoholic and had not been exposed to toxins. A familial neuropathy, such as Charcot–Marie–Tooth disease, is a possibility, but his neuropathy was recently acquired. He had no family history and did not have high arches. Small fiber involvement is not typical but can occur in this disorder. A chronic inflammatory demyelinating polyneuropathy (CIDP) is a consideration because, although patients with CIDP usually have mostly large fiber involvement, pain and temperature sensory deficits can also be present. CIDP associated with a monoclonal gammopathy and with AIDS is also a consideration. He did not have a history of a connective tissue disease, and the slow progression is against a vasculitic neuropathy. Porphyric neuropathy is unlikely because this usually presents with intermittent attacks and affects mainly motor axons.

Laboratory studies included a normal erythrocyte sedimentation rate; complete metabolic panel, complete blood count, B ₁₂ /folate, HIV, immunoelectrophoresis, thyroid-stimulating hormone, and fluorescent antinuclear antibody were all normal.