Case report of anti‑IgLON5 disease presenting as Pisa syndrome with strong anti‑IgLON5 antibody positivity and marked clinical improvement after rituximab over 24 months.

Useful clinically because it highlights an immune‑mediated mimic of a Parkinsonian postural deformity and responsiveness to B‑cell immunotherapy, but offers limited direct mechanistic or broad therapeutic discovery insight for Parkinson's disease.

Pisa syndrome, characterized by lateral flexion of the trunk, is most often associated with neuroleptic use or neurodegenerative disorders like Parkinson's disease. Anti-IgLON5 disease is a rare neuroimmunological condition with overlapping features of autoimmunity and tauopathy, manifesting with sleep and cognitive disturbances, bulbar symptoms, and movement disorders. We report a 50-year-old man who presented with progressive lateral trunk flexion, head drop, dysarthria, and choreiform movements. The classic features of antiIgLon 5 disease including sleep and cognitive disturbances were absent. Serum testing confirmed strong positivity for anti-IgLON5 antibodies. Treatment with rituximab led to marked clinical improvement, with amelioration of symptoms at 24 months. This case illustrates an uncommon presentation of anti-IgLON5 disease as Pisa syndrome. Recognition of this association is important, as early immunotherapy can significantly improve outcomes in an otherwise progressive and disabling condition.