Focal lipoatrophy.

Focal atrophy of a limb is usually caused by loss of muscle due to nerve or muscle disease. However, focal atrophy of subcutaneous tissues, an uncommon but well described entity, can mimic neuromuscular disease by producing a similar appearance of the limb. The clinical sign of thinness of the subcutaneous tissues (the "pinch-an-inch" test) suggests lipoatrophy as the cause of the limb asymmetry.