(BMJ)—A 58-yo woman w/ hx of RA presented w/ a sudden inability to use her R thumb after trying to tear open a dishwasher tablet package. Exam: R thumb in dropped position. Able to abduct, adduct, oppose, and flex but not extend. Her hand was neurovascularly intact. What is the dx?
Radial nerve palsy
Extensor pollicis longus rupture
Posterior interosseous nerve injury
Adductor pollicis longus rupture
De Quervain tenosynovitis
You are correct. The dropped appearance of her thumb suggested damage to the extensor mechanism of the thumb, consistent w/ extensor pollicis longus (EPL) rupture. EPL rupture leads to a flexion deformity of the interphalangeal joint and inability to extend the distal phalanx. Although the adductor pollicis longus (APL) is also involved in extension, there was no loss of ability to abduct, indicating the APL was intact. Lack of pain or signs of inflammation ruled out de Quervain tenosynovitis. EPL rupture is seen w/ distal radial fractures, but spontaneous rupture is possible and assoc w/ systemic lupus erythematosus or RA. This pt was referred to plastic surgery for tendon transfer.

Emergency Medicine Journal 2019;36:224-238