Spinocerebellar degenerations and ataxias
Definition: Spinocerebellar degenerations and ataxias are a group of progressive neurodegenerative disorders affecting the cerebellum, spinal cord, and their connections, leading to ataxia (loss of coordination).
- They may be hereditary (most common in spinocerebellar ataxias) or acquired.
Classification
- A. Hereditary Ataxias (Spinocerebellar Ataxias – SCA): Autosomal dominant (most SCAs). Autosomal recessive (e.g., Friedreich ataxia)
- B. Acquired Ataxias: Alcoholic cerebellar degeneration. Multiple sclerosis. Tumors (posterior fossa). Stroke (cerebellar infarction). Vitamin deficiencies (B1, B12, E). Toxic (drugs, alcohol)
Pathogenesis
Damage to: Cerebellar cortex. Spinocerebellar tracts. Posterior columns
➡️ Leads to disruption of coordination of movement, posture, and balance.
Clinical Features (Cerebellar Syndrome)
- A. Gait and Trunk Ataxia: Wide-based gait. Unsteady walking. Difficulty standing upright
- B. Limb Ataxia: Intention tremor. Dysmetria (past-pointing). Dysdiadochokinesia (impaired rapid alternating movements)
- C. Speech Disturbance: Scanning (staccato) speech. Slurred articulation
- D. Eye Movement Disorders: Nystagmus. Gaze-evoked oscillations
- E. Hypotonia: Decreased muscle tone. Pendular reflexes
Specific Types
- A. Friedreich Ataxia (Autosomal Recessive)
Pathology
- Degeneration of: Spinocerebellar tracts. Posterior columns. Corticospinal tracts
Clinical Features: Onset in childhood/adolescence. Progressive ataxia. Loss of vibration and position sense. Weakness. Absent reflexes (early), later spasticity. Cardiomyopathy (important systemic feature)
Key Sign: Sensory + cerebellar ataxia
- B. Spinocerebellar Ataxias (SCA types)
Features: Autosomal dominant. Adult onset. Progressive cerebellar ataxia. Variable pyramidal and extrapyramidal signs
- C. Alcoholic Cerebellar Degeneration: Mainly affects anterior superior cerebellar vermis. Gait ataxia predominant. Lower limb coordination affected more than upper limbs
Examination
Cerebellar Tests
- Finger-to-nose test → dysmetria
- Heel-to-shin test → ataxia
- Rapid alternating movements → dysdiadochokinesia
- Romberg test → usually negative (pure cerebellar lesion)
Diagnosis
- Clinical Diagnosis: Based on cerebellar signs + progression pattern
- MRI Brain: Cerebellar atrophy. Vermis degeneration (alcoholic type). Brainstem atrophy in hereditary forms
- Genetic Testing: For spinocerebellar ataxias (SCA types)
Differential Diagnosis
- Sensory Ataxia: Positive Romberg sign. Loss of vibration sense
- Vestibular Ataxia: Vertigo. Nystagmus. Falls to one side
- Multiple Sclerosis: Multifocal CNS signs
- Stroke: Sudden onset cerebellar signs
Treatment
- General: No curative therapy for most hereditary forms
- Symptomatic: Physiotherapy. Occupational therapy. Speech therapy.
- Treat Underlying Causes: Alcohol cessation. Vitamin replacement (B1, B12, E). Tumor removal if present