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Carpal tunnel release with some residual thenar atrophy
6%
52/854
Corticosteroid injection with temporary improvement in symptoms
7%
59/854
Observation with gradual functional improvement over a one year period
84%
719/854
Referral to psychiatry for conversion disorder with improvement after therapy
1%
5/854
Tendon transfers with residual deficit in hand function
10/854
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Anterior interosseous nerve (AIN) syndrome is relatively uncommon and may occur secondary to viral neuritis such as Parsonage-Turner Syndrome. Without a known history of trauma to the forearm, the most appropriate initial management is observation alone. The AIN is a motor nerve responsible for innervation of the flexor pollicis longus, flexor digitorum profundus to the index and middle fingers, and pronator quadratus. It branches off the median nerve 5-8cm distal to the lateral epicondyle where it passes between the two heads of the pronator teres and thereafter traveling just volar to the flexor digitorum profundus muscle bellies. Its does not serve any sensory function and terminates in the pronator quadratus muscle belly. Its function is assessed on physical examination by having the patient perform the “A-OK” sign. If there is a suspected direct laceration or penetrating injury to the AIN, surgical exploration should be employed with primary nerve repair in a timely manner. Non traumatic causes of AIN syndrome warrant an initial period of observation for clinical improvement. Sood and Burke retrospectively reviewed 16 patients with partial or complete AIN palsy. They stressed the importance of distinguishing isolated motor symptoms to establish the diagnosis. Any associated neurologic lesions, such as loss of sensation, suggests multifocal pathology of non-compressive origin such as brachial plexus neuritis/injury. They conclude that surgical exploration is only indicated in patients with penetrating injuries or complete AIN palsies with no signs of recovery after 6 months of conservative treatment. Chi and Harness reported their case series of twenty-one patients with AIN palsy treated non-surgically. All patients displayed complete or near complete recovery by 18 months. The authors conclude in the absence of discrete, verifiable pathophysiology, surgical exploration and decompression should be avoided until at least 1 year from the onset of symptoms. Incorrect Answers: Answer 1. Carpal tunnel release would be indicated if there was median nerve compression at the level of the wrist. This patient has acute onset motor nerve symptoms without paresthesias, which is suggestive of AIN syndrome. Releasing the transverse carpal ligament is not indicated in this setting. Answer 2. There is no current data in support of corticosteroid injections in the setting of AIN syndrome. Answer 4. While conversion disorder is on the list of differential diagnoses, this patient has clear objective evidence of AIN syndrome based on her electrodiagnostic studies. Answer 5. Tendon transfers would be considered after exhaustive treatment in which functional recovery is deemed futile.
5.0
(3)
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