A Case of Non-traumatic Extensor Pollicis Brevis PalsyNate Minnick, D.O.Emergency Medicine Resident St. John Hospital and Medical Center A 38 year old female presented to the emergency department with a non-traumatic extensor pollicis brevis palsy. It presented as a prime opportunity for a medical student to work through the physical exam of an isolated hand muscle dysfunction due to an unusual etiology. Isolated extensor pollicis brevis injuries are rare without preceding trauma. They can be treated conservatively with anti-inflammatory medications and activity modification. Surgical therapy is the last, definitive treatment. Posterior interosseous nerve entrapment should be considered whenever carpal tunnel syndrome is part of a differential in a patient’s workup. A 38 year old female presented to the emergency department (ED) with left hand numbness. She complained of a change in sensation in her left thumb that she noticed for the past three days. Although the triage report stated “left hand numbness”, the patient claimed that numbness wasn’t the correct term, her thumb and index finger “didn’t feel right”. Other fingers were not involved, she denied any injury, but did notice that there was some weakness when moving her left fingers. There was no neck, shoulder, arm, or wrist pain. She admitted to a lot of stress, as she was traveling to start a new job in a different state, and had been in town for only a few days visiting a friend, and would be driving across the country the next day. Her job consisted of constant computer usage. She denied any past medical history, past surgery, took no medications, and had no allergies.
On exam, the patient appeared her stated age, acted mildly anxious, but
otherwise appeared well. Vital signs were stable. She had a supple neck
with no tenderness, and a negative Lhermitte’s. Her left forearm and
hand had no deformities and no palpable bony defects, with no tenderness
caused by palpation. Radial pulse was intact and regular. The biceps,
triceps, and brachioradialis reflexes were 2+ bilaterally. She had slightly diminished grip strength of the left hand when compared to the right. When passively extending the left thumb, the patient could not keep it extended against any resistance, yet had 5/5 strength in flexion. The patient had a difference in subjective light touch to the palmar surface of the left thumb compared to the right, but did have equal subjective sensation to all parts of the dorsal hand. She had no difference in light touch to the right thumb, hand surfaces or fingers.
Tinel’s test, median nerve compression, Phalen’s test, and Finkelstein’s
test were all negative. Whereas non-traumatic dysfunctions of isolated extensor muscles in the arm and hand are rarely reported, radial nerve entrapment in general has a more frequent occurrence. Radial nerve entrapment is commonly known as the “Saturday night palsy”, but is less common than median nerve compression and ulnar nerve compression at the elbow. Injury to the radial nerve results in loss of wrist extension, digit extension, and thumb extension. The posterior interosseous nerve (PIN) is a continuation of the radial nerve after crossing through the supinator muscle. It bifurcates into a medial and a lateral/deep branch[1]. The medial branch innervates the extensor carpi ulnaris, extensor digiti quinti, and extensor digitorum communis. The lateral/deep branch innervates the abductor pollicis longus, extensor pollicis brevis, extensor pollicis longus, and extensor indicis proprius. The extensor pollicis brevis runs from the posterior radius and inserts at the posterior/dorsal proximal phalanx of the thumb. Its action is to extend the thumb; it contributes some abduction action. PIN compression occurs most often in the area of the supinator muscle, resulting in the name “supinator syndrome”. Cravens and Kline found that thirty-two patients with PIN disorders were caused by entrapment, compression, or tumor, or as a result of trauma in the form of contusion, laceration, fracture.[2] Compression occurs due to repetitive activities that involve wrist supination and pronation [3]; Molloy et al. found a high prevalence in professional America’s Cup sailors.[4].
The brachioradialis and extensor carpi radialis brevis/longus muscles,
which are innervated by more proximal branches of the PIN, are spared in
PIN entrapment.[5] It is widely reported that pain is absent or minimal
in patients with entrapment; no sensory deficit is typical, but some
amount of motor paralysis of the extensor muscles is reported.[2,4,5]
Radial tunnel syndrome differs from PIN entrapment in that lateral
forearm pain is severe, and motor weakness is slight or absent.[3]. Suematsu and Hirayama found eight of eleven patients with PIN entrapment had compression at the entrance of the supinator muscle, causing “drop thumb” and “drop finger” paralysis, in that many different extensor muscles were affected.[1] Three patients had compression at the exit resulting in either a dropped thumb or a dropped finger, involving a more limited and digit-specific paralysis. The limitation of either finger or thumb involvement seems to result from anatomical variation of the musculotendinous membrane of the supinator muscle.[6].
Conservative treatment of immobilization, functionally splinting and
anti-inflammatory medications are the first line of treatment for PIN
entrapment, and surgical therapy can be provided depending on the
patient’s results. Surgical therapy appears to have a high curative
rate, with one study finding a 96% success in absolving paralysis. [5].
This is a rare case of a non-traumatic extensor pollicis brevis palsy.
In addition to a gross motor deficit, she had minor symptoms of
sensation change, which is congruent with research on PIN
entrapment.[2,4,5] The ER physician’s role in cases of PIN entrapment is
to rule out vascular insufficiency, compartment syndrome, and trauma,
and then to provide symptomatic relief as best possible, finally
referring the patient to an orthopedic surgeon or neurologist.
Unfortunately the patient left the state, making follow-up difficult. If
activity modification and a course of NSAIDs did not relieve her
symptoms, surgical nerve release/decompression would have been
warranted. # # # Posted:
Wednesday, October 19, 2011
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