Dystonia commonly involves contraction of which muscle group?

• A. Sternocleidomastoid muscles
• B. Quadriceps
• C. Latissimus dorsi
• D. Gastrocnemius

Answer: (A)

Dystonia presents with involuntary, sustained or repetitive muscle contractions that produce abnormal postures or movements. When dystonia affects the neck, the contraction pattern most often involves the sternocleidomastoid muscle. The SCM is a key neck muscle that rotates and flexes the head; overactivity of this muscle can pull the head into twisting or tilting positions, which is the hallmark of cervical dystonia. The other muscles listed—quadriceps and gastrocnemius in the legs, and latissimus dorsi in the back—are not the typical drivers of the characteristic neck postures seen in cervical dystonia. So the sternocleidomastoid is the muscle group most commonly involved.