To describe hemidystonia as a rare neurologic manifestation of primary antiphospholipid syndrome (APS) and highlight diagnostic and management challenges.

Antiphospholipid syndrome (APS) is an autoimmune hypercoagulable state. While chorea is the most frequently reported movement disorder in APS, occurring in approximately 1.3% of cases, hemidystonia is a rare manifestation typically resulting from ischemic or microvascular insult to the contralateral basal ganglia or thalamocortical circuits.

A 25-year-old male with a history of primary APS, systemic lupus erythematosus, and recurrent deep vein thrombosis presented with chronic left-sided hemidystonia and episodic, severe pain. Physical examination during symptomatic episodes revealed characteristic dystonic features: the left hand demonstrated a combination of forced finger extension and flexion, while the left foot exhibited sustained hyperextension (striatal toe). These findings were accompanied by tonic contraction of the left trapezius. Outside of these paroxysmal episodes, the patient exhibited baseline choreiform and tic-like movements. Clinical history revealed a temporal correlation between symptom exacerbations and periods of sub-therapeutic anticoagulation, including a recent thrombosis of an iliac venous stent.

The diagnosis of APS-related hemidystonia was made based on the patient’s known hypercoagulable state and the failure of alternative diagnoses. The hemidystonia was unresponsive to standard GABA-enhancing medications (benzodiazepines, gabapentin) and intensive immunotherapies, including IVIG and plasmapheresis. However, the patient reported significant symptomatic relief with diphenhydramine and was successfully transitioned to trihexyphenidyl. Management focused on secondary prevention by maintaining an aggressive high-intensity anticoagulation target with an INR of 3.0–4.0.

This case identifies hemidystonia as a primary organic manifestation of APS, likely driven by cumulative microvascular or ischemic injury. Management should focus on aggressive anticoagulation to prevent neurological progression and the use of anticholinergic therapy for symptomatic relief. A high index of suspicion is required to differentiate these organic posturing events from other paroxysmal movement disorders in the context of autoimmune disease.