Spontaneous anterior interosseous nerve palsy with Churg–Strauss syndrome

A 74-year-old woman diagnosed with Churg–Strauss syndrome (CSS) complained of difficulty in flexing her left thumb and index finger. Electromyography demonstrated isolated anterior interosseous nerve (AIN) palsy, with no other peripheral neuropathy. We diagnosed this case as spontaneous AIN palsy complicated with CSS, the first case of this kind. Surgical treatment should be considered if no sign of recovery is seen within six months of onset.