What is the characteristic symptom of myotonic muscular dystrophy?

Myotonic muscular dystrophy is specifically characterized by myotonia, which refers to the inability of muscles to relax after contraction. This slow relaxation of muscles is due to abnormal ion channel function, leading to prolonged muscle contraction. Patients with this condition frequently experience stiffness and difficulty relaxing their muscles, which can manifest following activities such as gripping or releasing objects.

While muscle weakness, joint stiffness, and cramps can be associated symptoms in some muscular dystrophies or neuromuscular disorders, they are not the hallmark feature of myotonic muscular dystrophy. The defining characteristic is indeed the slow relaxation of muscles after contraction, making it the most accurate choice in relation to this specific condition.