Abrupt-onset cervico-truncal dystonia after Mycoplasma pneumoniae infection: Unmasking a possible CACNA1A-related susceptibility

Cervico-truncal dystonia has been described in association with infectious or post-infectious processes, including Mycoplasma pneumoniae. However, the contribution of underlying genetic susceptibility in such presentations remains poorly defined. We report the extended follow-up of a 32-year-old man who developed abrupt-onset cervico-truncal dystonia three weeks after a febrile upper respiratory tract infection associated with Mycoplasma pneumoniae. Given the atypical course and lack of sustained response to immunomodulatory therapies, whole-exome sequencing was performed, followed by application of a virtual multigene panel for movement disorders. Variant interpretation was conducted according to ACMG/AMP criteria, and segregation analysis was performed by Sanger sequencing. Despite initial improvement after intravenous immunoglobulins, the patient experienced recurrence and persistence of dystonic symptoms, with no evidence of ongoing inflammation. Genetic analysis identified a novel heterozygous frameshift variant in the CACNA1A gene, predicted to result in loss of function and classified as pathogenic. The variant was inherited from an asymptomatic mother, supporting incomplete penetrance. These findings suggest that the infectious event may have acted as a trigger, unmasking an underlying channelopathy. Dystonia is not a typical manifestation of CACNA1A-related disorders and has only rarely been reported; therefore, this case may support a possible expansion of the phenotypic spectrum rather than indicate a common CACNA1A-associated dystonia phenotype.