Torsion dystonia is a rare movement disorder characterized by involuntary spasmodic contractions of the muscles of the legs, trunk, arms, and face, leading to twisting of the affected body part and often a distorted or contorted appearance. Muscle contractions (posturing) typically start in a single part of the body (eg, leg, foot, arm) and may spread to other body parts over time, usually first to contiguous sites.

With progression, these disorders can result in fixed postures with difficulty moving the affected body parts and severe limitation of function. Associated signs and symptoms may include dysarthria, dysphagia, hyperreflexia, joint contractures, and tremors. The condition can occur sporadically or be inherited, most often in an autosomal dominant manner. There are over 20 known genetic mutations identified as causes of dystonia, each with variable onset, associated symptoms, and prognoses. Some of the most notable disorders are:

• DYT1 (Oppenheim dystonia): Autosomal dominant, early onset (before age 40), typically affecting one limb first and spreading to other sites.
• DYT5 (Dopa-responsive dystonia): Autosomal dominant, childhood onset (before age 16), symptoms typically start in the leg, diurnal variation in symptoms (worse at night), associated parkinsonism, marked improvement with low-dose levodopa.
• DYT6: Autosomal dominant, child and adult onset, typically starts in the arm or cranial region, and involvement usually remains in the upper body.
• DYT11 (Myoclonus dystonia): Autosomal dominant, typically affects the upper body and spares the legs.
• DYT12 (Rapid-onset dystonia-parkinsonism): Autosomal dominant, adolescent and adult onset, parkinsonism present, dystonia generalizes over hours to weeks and then plateaus, involvement of speech.