What is the primary characteristic of dystonia?

The primary characteristic of dystonia is uncontrollable muscle contractions that lead to twisting and repetitive movements or abnormal postures. These involuntary movements can occur in different parts of the body, including the face, neck, and limbs. In the context of the choices provided, uncontrollable teeth grinding, also known as bruxism, can occur as a motor symptom of dystonia, specifically in cases affecting the jaw muscles.

Dystonia can manifest in various forms, and while it is distinguished by its patterned muscle contractions, it does not directly cause significant weight loss, extreme fatigue, or persistent insomnia as primary symptoms. These other options may arise from various medical or psychological conditions but do not encapsulate the defining feature of dystonia. The involuntary muscle contractions leading to teeth grinding align with the hallmark symptoms of dystonia, making it the most accurate option.