In toddlers, parents may notice enlarged calf muscles (see image at right). This enlargement is known as pseudohypertrophy, or "false enlargement," because the muscle tissue is abnormal.

Why is it called Duchenne?

Psychologists call this the “Duchenne smile,” and most consider it the sole indicator of true enjoyment. The name is a nod to French anatomist Guillaume Duchenne, who studied emotional expression by stimulating various facial muscles with electrical currents.

What is meant by Pseudohypertrophy?

Pseudohypertrophy, muscular enlargement through deposition of fat rather than muscle fibre, occurs in other forms of muscular dystrophy, particularly the Duchenne type.