Picture quiz: answer

While peripheral lesions account for a significant proportion of cases presenting with isolated motor hand weakness (Box 1), this case illustrates the importance of recognizing infarction of the hand knob area as a cause for such a presentation. An accurate history is essential, along with a detailed systemic and neurological examination performed, particularly looking for other neurological findings that may hint towards a peripheral cause or involvement of more areas cortically. The presence of weakness of all muscle groups is unusual in peripheral nerve lesions and led in this case to the initial investigation with cerebral MRI, which provided the diagnosis.