[Anterior Interosseous Nerve Palsy with Isolated Flexion Palsy of the Thumb or Index Finger as an Initial Symptom:Two Case Reports].

Case 1: A 73-year-old man who had undergone neurolysis for right cubital tunnel syndrome complained of difficulty using chopsticks. Froment's sign test showed that the interphalangeal(IP)joint of the right thumb that had flexed preoperatively was extended. This finding was considered to indicate recovery from ulnar neuropathy, and the patient was closely followed up. One year later, the patient was unable to push a camera shutter button and was unable to flex the IP joint of the thumb and the distal interphalangeal(DIP)joint of the index finger, a characteristic symptom of anterior interosseous nerve(AIN)palsy. Therefore, the patient underwent AIN neurolysis and subsequently reported slight improvement in his condition. Case 2: A 60-year-old woman reported difficulty performing computer mouse clicks with her right hand. As flexing the index finger DIP joint was difficult, a local lesion was suspected, and the patient was closely followed up. One year later, the patient was unable to push the button of a ballpoint pen with her thumb. Extension of the thumb and index finger indicated AIN palsy. The patient refused treatment and was only followed up. The following year, the patient reported that the weakness improved. Simultaneous flexion palsy of the thumb and index finger can lead to a diagnosis of AIN palsy. However, flexion palsy of a single finger in incomplete AIN palsy, as reported here, is often overlooked because of its similarity to the flexor tendon rupture. Awareness regarding this incomplete form of AIN palsy is needed for early and correct diagnosis.