Case 16

Published on 03/03/2015 by admin

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Last modified 03/03/2015

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Case 16

HISTORY AND PHYSICAL EXAMINATION

Acute, severe right upper extremity pain developed overnight in a 22-year-old man; it peaked in 2 days, resulted in multiple visits to the emergency room, and ultimately led to admission to a community hospital on the third day. The pain was deep and maximal around the right shoulder, with radiation to the arm and forearm, and did not worsen with coughing or sneezing. Three to four days after admission, while the patient was being treated with analgesics, he noted weakness of the right upper extremity. The weakness was maximal in the shoulder and arm, and much less severe in the hand. He had slight numbness in the hand and forearm, most particularly in the right thumb. He was given a 10-day course of oral prednisone and was referred to a tertiary care center.

Two weeks before the onset of pain, the patient had an upper respiratory tract infection with cough, nasal discharge, fever, and malaise. This was treated with antibiotics for one week. There was no history of trauma. He was otherwise in excellent health.

When the patient was seen 4 weeks after the onset of symptoms, he had minimal shoulder pain. Cranial nerve examination was normal. There was no Horner sign. Findings were limited to the right upper extremity, where there was complete loss of function of the right deltoid, spinati, biceps, and brachioradialis (Medical Research Council [MRC] 0/5). The right triceps was much less involved (4/5). There was mild diffuse weakness of all finger and wrist extensors, with severe weakness of the right thumb long flexion (flexor pollicis longus) and distal interphalangeal flexion of the index and middle fingers (flexor digitorum profundus). This resulted in a positive pincer or OK sign (Figure C16-1). Deep tendon reflexes of the right upper limb were absent. Sensation revealed mild sensory loss over the thumb, and lateral arm and forearm.

An electrodiagnostic (EDX) study was performed.

Please now review the Nerve Conduction Studies and Needle EMG tables.

EDX FINDINGS AND INTERPRETATION OF DATA

Abnormalities on EDX examination include:

The aforementioned findings point to a diffuse, likely multifocal process involving the neural elements of the upper extremity, with the most severe involvement to the upper trunk of the brachial plexus and the anterior interosseous nerve. The process is not the result of root(s) pathology (i.e., it is not due to intraspinal canal process), because of abnormal SNAPs and normal paraspinal muscles. The EDX findings are highly suggestive of neuralgic amyotrophy due to the predilection of lesions to the upper trunk and the anterior interosseous nerve.

DISCUSSION

Clinical Features

Neuralgic amyotrophy is likely an immune-mediated disorder that affects peripheral nerves of the upper limb and is not restricted to elements of the brachial plexus. Unfortunately, the disorder is known by several misleading names that result sometimes in misdiagnosis (Table C16-1). Neuralgic amyotrophy has an estimated annual incidence of 1.64 cases per 100 000 population. It most often affects adults, peaking during their twenties. Males are affected twice as often as females. It is usually unilateral, but is sometimes bilateral and asymmetrical; it is occasionally recurrent. Most cases have no specific precipitating factors, but some appear few hours to weeks of an upper respiratory tract infection, a vaccination, childbirth, or an invasive diagnostic, therapeutic or surgical procedure.

Table C16-1 Terms Commonly Used to Describe the Syndrome of Neuralgic Amyotrophy (Listed Alphabetically)

As the most popular name implies, neuralgic amyotrophy is characterized by pain and weakness of the upper limb. The pain is usually abrupt in onset with a tendency to develop at night, sometimes awakening the patient from sleep. It is a severe deep boring shoulder pain, and maximal during the first few days of illness. The pain is not exacerbated by the Valsalva maneuver (e.g., cough, sneeze) which helps distinguishing it from a subacute cervical radiculopathy. Many patients visit the emergency department for pain control. In atypical cases, the pain is only modest and maximal over the antecubital fossa. The pain usually lasts for 7–10 days, gradually fades and becomes replaced by a dull ache.

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