A 57-year-old woman with breast carcinoma developed right upper extremity weakness.

This 57-year-old woman was evaluated for weakness of the right arm and hand. She had previously undergone a right mastectomy and chemotherapy for breast cancer. Because of recurrent tumor, she received additional chemotherapy and had radiation therapy to the right shoulder/axilla. She consulted us because of right arm and hand weakness and pain under her right scapula.

Examination showed no evidence of a Horner syndrome. There was atrophy of her right forearm and weakness of multiple muscles of the right upper extremity including the supraspinatus, deltoid, biceps, brachioradialis, triceps, wrist and finger extensors, finger flexors, and multiple intrinsic hand muscles. Triceps and wrist extensor weakness was especially severe. Muscle stretch reflexes in both arms were diffusely hypoactive. A trace triceps reflex was noted on the left, but none on the right. Pinprick sensation was diminished on the right thumb, middle finger, and medial forearm.

Electromyography (EMG)/nerve conduction studies were abnormal with acute denervation changes noted in muscles innervated by multiple nerves and mild abnormalities noted on median and ulnar motor and sensory nerve conductions. These findings were most indicative of an acute brachial plexopathy. No myokymia was noted. Magnetic resonance imaging (MRI) of the right axilla/brachial plexus demonstrated axillary lymphadenopathy. The patient was diagnosed with right brachial plexopathy due to metastatic lymphadenopathy.