Misleading EEG in CACNA1A mutation: A case of late-onset episodic ataxia type 2.

BACKGROUND: Episodic ataxia type 2 (EA2) is a rare, autosomal dominant paroxysmal neurological disorder caused by mutations in the CACNA1A gene. Its hallmark features include transient episodes of ataxia and dysarthria, often responsive to acetazolamide. However, misdiagnosis as epilepsy may occur due to overlapping electroencephalographic findings.

CASE PRESENTATION: We report a 64-year-old woman with no prior history nor family history of neurological illness, who developed daily episodes of dysarthria and ataxic gait. Brain MRI did not show definite signs of cerebellar atrophy. Interictal EEG demonstrated sharp waves in the left temporal region, initially leading to a diagnosis of focal epilepsy. Despite trials of multiple antiseizure medications, symptoms worsened. Subsequent ictal EEG and SPECT showed no definitive seizure activity or clinical correlation. Genetic testing identified a heterozygous CACNA1A splice site variant (NM_001127222.2: c.2280-2A > T), confirming EA2. Tapering of antiseizure therapy and initiation of acetazolamide resulted in sustained symptom resolution.

DISCUSSION: This case underscores the diagnostic challenge posed by interictal EEG abnormalities in CACNA1A-related disorders. While such findings may suggest epilepsy, they can be misleading in the absence of clinical epileptic seizures. Recognition of EA2 and judicious use of genetic testing facilitated accurate diagnosis and effective treatment. Clinicians should be cautious in interpreting EEG in patients with paroxysmal neurologic symptoms and prioritize clinical correlation to avoid inappropriate therapy.