Objective: To report an unusual phenotype of spinocerebellar ataxia 17 (SCA17) with childhood onset epilepsy evolving into asymmetric motor impairment with features of dystonia and myoclonus.

Background: SCA17 is a rare autosomal dominant progressive disease in the group of polyglutamate disorders caused by CAG/CAA repeat expansions in the TATA-box binding protein (TBP) gene leading to a neurodegenerative disease with a heterogenous and variable phenotype.

Method: Chart review and literature search was performed.

Results: A 62-year-old Caucasian male with a history of focal epilepsy since age 4 presented to our clinic for consideration of surgical management. His medical history was notable for nephrolithiasis, prior tobacco use, coronary artery disease and bilateral cataracts. Family history was negative for neurological disease save stroke in his father. In addition to his seizure disorder he also reported right upper extremity incoordination and tremor since age 55.

Initial neurological examination solely demonstrated mild intention tremor in the right>left upper extremities. Routine EEG showed left temporoparietal sharp waves. Brain MRI showed right mesial temporal sclerosis with multiple areas of volume loss in the superior aspects of both cerebellar hemispheres and focal volume loss in the right occipital lobe. He was treated with levetiracetam and lamotrigine and did not pursue epilepsy surgery. 

The patient was lost to follow up due to the COVID pandemic but upon return his exam showed worsening tremor, ataxia, right upper extremity dystonia and abnormally slow saccades. Serum and CSF studies for infectious, autoimmune and paraneoplastic etiologies were unrevealing. Fragile X testing and a limited SCA panel were negative. Dopamine transporter scan (DATSCAN) was normal and he had no response to an empiric trial of carbidopa/levodopa. Neuropsychological testing was normal. As his symptoms progressed further genetic testing showed a 41 CAG/CAA repeat expansion in the TBP gene (STUB 1 gene negative).

Conclusion: The presented case suggests that 41 CAG/CAA trinucleotide expansion can be considered a critical threshold in SCA17. We suggest that SCA 17 should be suspected in patients with movement disorders associated with epilepsy. While seizures may be part of the SCA 17 phenotype, we are not aware of any reports in the literature demonstrating mesial temporal sclerosis with hippocampal atrophy in this disease.

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MDS Abstracts - https://www.mdsabstracts.org/abstract/spinocerebellar-ataxia-17-presenting-with-childhood-seizures-and-mesial-temporal-lobe-sclerosis/