During examination of a patient with cerebellar syndrome, the physician tests for intention tremor by asking the patient to perform finger-to-nose testing. Which is the most common cause of cerebellar dysfunction presenting with intention tremor in India?

Explanation

## Most Common Cause of Cerebellar Dysfunction in India **Key Point:** Spinocerebellar ataxias (SCAs), particularly SCA2 and SCA3, are the most common inherited cause of progressive cerebellar dysfunction presenting with intention tremor in the Indian population. ### Epidemiology in India - **SCA2** and **SCA3** (Machado-Joseph disease) are the most prevalent SCAs in India - Autosomal dominant inheritance with CAG trinucleotide repeat expansion - Progressive neurodegenerative course with onset typically in 3rd–5th decade - High prevalence in certain regions (Tamil Nadu, Kerala, Andhra Pradesh) ### Clinical Features of SCA | Feature | Presence in SCA | | --- | --- | | **Intention tremor** | Yes (prominent) | | **Gait ataxia** | Yes (early and progressive) | | **Dysarthria** | Yes (scanning speech) | | **Nystagmus** | Yes (often present) | | **Ophthalmoplegia** | Yes (especially SCA3) | | **Pyramidal signs** | Yes (variable) | | **Progressive course** | Yes (over years to decades) | ### Why SCA is Most Common (Comparative Context) 1. **SCA vs. Stroke:** Stroke is acute; SCA is chronic and progressive. The question implies a syndrome (examination findings), suggesting chronic pathology. 2. **SCA vs. MS:** MS is rare in India; SCAs are endemic. MS typically presents with optic neuritis, myelitis, or brainstem signs before cerebellar involvement. 3. **SCA vs. SDH:** Subdural hematoma is acute/subacute with headache, altered consciousness, focal deficits—not a pure cerebellar syndrome. **High-Yield:** In an Indian patient with **progressive intention tremor + ataxia + dysarthria + nystagmus**, think **SCA2 or SCA3** first. Genetic testing (CAG repeat expansion) confirms diagnosis. **Mnemonic:** **SCAN** = **S**pinoCerebellar **A**taxia is most **N**otable in India. **Clinical Pearl:** SCA3 (Machado-Joseph disease) often presents with external ophthalmoplegia and pyramidal signs in addition to cerebellar features, making it a distinctive variant in Indian populations. [cite:Harrison 21e Ch 387; Neurological Disorders in India, ICMR consensus]