A Man With a Long History of Muscle Weakness in One Arm

A 35-year-old man presented with complaints of pain in the left shoulder and neck. Over the next 4 years, he developed progressive proximal left arm weakness and marked atrophy of the left shoulder girdle. Despite several evaluations during the next 3 years, including a normal myelogram, the etiology for his weakness was unclear, but the symptoms did not spread.

He presented for a disability evaluation 12 years after the onset of symptoms, which had remained stable and did not progress. He denied previous neck or shoulder trauma. He had no bladder/bowel or sensory complaints, sexual dysfunction, or any history of diabetes, poliomyelitis, or surgery. He had occasional tingling in all of the fingers of the right hand with intermittent dull pain in his right forearm.

General examination showed a well-developed, well-nourished man in apparent good health. Mental status, cranial nerves, and sensory testing were normal.

Examination of the left upper extremity and shoulder girdle revealed a full range of passive motion with minimal shoulder tenderness at the extremes of abduction and external rotation. He had prominent atrophy in his left shoulder girdle ( Fig. 33A-1 ). There was prominent left upper extremity proximal weakness; the deltoid and infraspinatus muscles were 2/5, the latissimus dorsi was 3/5, pectoralis, biceps, and brachioradialis 4/5, and triceps were 4+/5. The left wrist and hand had normal strength. His right arm and bilateral leg strength was normal.

Reflexes were brisk in the left upper extremity and were normal in the right upper extremity and both legs. Toes were downgoing. No pathologic reflexes or spasticity were noticed.

What are the Differential Diagnoses?

This patient had a segmental disorder of the left upper extremity; the differential diagnosis includes a focal spinal cord lesion (such as a tumor, syringomyelia, or radiculopathy), but the lack of sensory findings, pain, or symptoms is against these. The lack of progression or spread is against a typical motor neuron disorder such as amyotrophic lateral sclerosis (ALS). Another possibility includes monomelic amyotrophy, a benign motor neuron disease. ¹ This condition usually affects one arm more distally. Other possibilities that need to be considered are a motor neuropathy, such as multifocal motor neuropathy, and also a multifocal axonal neuropathy. These, however, usually affect distal muscles. The lack of sensory findings argues against other focal neuropathies or plexopathies.

An EMG Test was Performed

Motor Nerve Studies

This case was reported in Metcalf JC Jr, Wood JB, Bertorini TE. Benign focal amyotrophy: metrizamide CT evidence of cord atrophy. Muscle Nerve . 1987;10:338–345.