Spinocerebellar ataxia 3 (SCA3)
General description
Spinocerebellar ataxia 3 (SCA3) also known as Machado-Joseph disease, develops in young to middle age caused by elongation of CAG repeat number in Ataxin 3 gene.
Initially, the disease is manifested by cerebellar ataxia, dysarthria, pyramidal tract symptoms, ocular motility difficulty, dystonia, and athetosis. Highly specific clinical findings include protruding eyes and action-induced facial and lingual fasciculations. The higher the number of CAG repeats, the more severe the symptoms.
References
- Kurokawa, Ryo, et al. "Clinical and neuroimaging review of triplet repeat diseases." Japanese Journal of Radiology 41.2 (2023): 115-130.
Atrophy
Atrophy starts in the cerebellum and extends to the pons and midbrain. Pontine atrophy involves both the tegmentum and the base of the pons.
Midline hyperintensity of Pons
Initially, there is atrophy of the cerebellum and a high T2WI signal in the median pons, reflecting degeneration of the transverse pontine fibers, but unlike the hot cross bun sign of Multiple system atrophy (MSA), the transverse pontine fiber degeneration is often only in the median.
Hyperintensity of Globus pallidus
Occasionally, linear high signal in the internal segment of the globus pallidus is observed on T2WI. PDWI reveals hyperintensity throughout the internal segment of the globus pallidus. This findings are useful for distinguishing Spinocerebellar Ataxia type 3 (SCA 3) from Dentatorubral-Pallidoluysian Atrophy (DRPLA). In SCA 3, the internal segment degenerates, whereas in DRPLA, it's the external segment.
Neuromelanin imaging
Neuromelanin imaging shows bilateral loss of hyperintensity in the substantia nigra.