A 56-year-old woman had a 4-month history of left shoulder and arm pain, and a 3-week history of numbness in the dorsum of the hand with some arm weakness. She awakened one morning with a wrist drop and was evaluated the next day by an orthopedic surgeon, who found a mass in the left arm. The patient had no systemic symptoms or history of trauma and no family history of neurologic disorders. She did have a history of hypertension and had undergone a decompressive laminectomy for a lumbar radiculopathy in the past.
Examination showed normal mental status and cranial nerves. She had severe weakness of the brachioradialis muscle, wrist, and finger extensors on the left. Strength of the triceps muscle was difficult to evaluate because of severe pain. The left brachioradialis reflex was absent, and ankle reflexes were diminished bilaterally; other reflexes were normal. There was decreased sensation in the left radial nerve distribution in the hand. The remainder of her neurologic examination was normal. There was a tender, indurated mass in the lower aspect of the left arm.
What is the Differential Diagnosis?
Wrist drop is usually caused by a lesion of the radial nerve. Wrist extensor weakness could also be caused by a C7 radiculopathy or a lesion of the middle trunk of the brachial plexus, but these conditions can also sometimes affect wrist flexion (through median and ulnar innervation). A posterior cord lesion can also cause a wrist drop. It also causes shoulder weakness from involvement of the axillary nerve.
Clinically, this patient appeared to have a radial neuropathy caused by compression from a mass in the arm. Other causes of a radial neuropathy in the arm include external compression, fractures of the humerus, inflammations, and infections. In this case the motor and sensory branches of the radial nerve were affected, but it was not clear if the triceps muscle was involved, because it was difficult to examine. The involvement of the radial sensory branch and weakness of the brachioradialis and extensor carpi radialis indicate a lesion of the main trunk of the radial nerve from the mass likely compressing the nerve, rather than a posterior interosseous neuropathy, which occurs at the elbow and is usually caused by fracture of the radius, entrapment at the supinator or extensor carpi radialis muscle, or posttraumatic injury.
An EMG Test was Performed
Motor Nerve Studies
This case was reported by Alzagatiti BI, Bertorini TE, Horner LH, Maccarino VS, O’Brien T. Focal myositis presenting with radial nerve palsy. Muscle Nerve . 1999;22:956–959.
