Cerebellar Ataxia Differential
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Direct answer
Cerebellar ataxia is an incoordination of gait, limbs and speech caused by damage to the cerebellum or its connections. The differential starts with the age of onset, the family history and whether the cause is hereditary, acquired or paraneoplastic. Friedreich ataxia is the commonest hereditary recessive ataxia, with early onset, areflexia, loss of position sense and hypertrophic cardiomyopathy, while alcohol, anticonvulsants and paraneoplastic antibodies such as anti-Yo cause acquired degeneration.
What you must remember
- Friedreich ataxia: autosomal recessive GAA repeat in the FXN gene, onset before 25 years, areflexia, extensor plantar responses, dysarthria, pes cavus and hypertrophic cardiomyopathy.
- Spinocerebellar ataxias: autosomal dominant, many due to CAG polyglutamine expansions such as SCA2 and SCA3 (Machado-Joseph), with reflexes variable (often preserved or brisk, but reduced in SCA2).
- Ataxia-telangiectasia: recessive ATM mutation with telangiectasia, immunodeficiency and raised serum alpha-fetoprotein.
- Alcohol: anterior vermal degeneration with gait and truncal ataxia out of proportion to limb signs; thiamine deficiency is often coexistent.
- Drugs: phenytoin and lithium cause ataxia, often reversible on stopping the drug.
- Gluten ataxia: sporadic cerebellar ataxia with anti-gliadin antibodies, which may occur without gut symptoms.
- Paraneoplastic ataxia: anti-Yo in women with ovarian or breast cancer, anti-Hu with small cell lung cancer, and anti-Tr with Hodgkin disease.
A clinical route through progressive unsteadiness
A 52-year-old man has six months of unsteadiness, slurred speech and a history of heavy alcohol use.
- Separate truncal from limb ataxia: Unsteadiness on sitting and standing with a wide-based gait points to the vermis, while limb dysmetria and intention tremor point to the hemispheres.
- Check for sensory ataxia: A positive Romberg sign or absent reflexes point to sensory or neuropathic ataxia instead, which is worth checking because the causes differ.
- Examine the eye movements: Eye movements are examined for saccadic dysmetria, square-wave jerks and gaze-evoked nystagmus.
- Read the pattern of atrophy: On brain MRI, vermian atrophy suggests alcohol, while global cerebellar and brainstem atrophy with autonomic failure suggests multiple system atrophy.
- Send the laboratory panel: TSH, vitamin B12, vitamin E, anti-gliadin and transglutaminase antibodies, HIV serology and a paraneoplastic panel are sent.
- Start treatment and keep screening: In this patient, the alcohol history makes thiamine replacement and abstinence the first treatment, while the paraneoplastic screen is still sent because the cerebellar syndrome may precede a tumour.
Where examiners test sensory versus cerebellar ataxia
The confusions below recur in examinations and cost marks in viva.
- Trap: taking a positive Romberg sign as proof of cerebellar ataxia. Correct: it points to sensory ataxia from posterior column or peripheral disease, since cerebellar ataxia does not depend on vision.
- Trap: confusing Friedreich ataxia with the spinocerebellar ataxias. Correct: early areflexia, extensor plantar responses and cardiomyopathy separate Friedreich ataxia.
- Trap: assuming every Friedreich-like picture is Friedreich ataxia. Correct: vitamin E deficiency can mimic it, which is a useful viva point.
- Trap: dismissing a paraneoplastic cause because the first scan is clear. Correct: cerebellar ataxia may precede the tumour by months, so a positive antibody deserves a cancer search.
Frequently asked questions
Which clinical sign separates cerebellar from sensory ataxia?
A positive Romberg sign, where balance worsens with the eyes closed, points to sensory ataxia from posterior column or peripheral disease. Cerebellar ataxia does not depend on vision and produces limb dysmetria, intention tremor and dysdiadochokinesia that cannot be explained by sensory loss.
What features distinguish Friedreich ataxia from other hereditary cerebellar ataxias?
Friedreich ataxia begins before 25 years, with areflexia in the legs, extensor plantar responses and loss of joint position sense. Hypertrophic cardiomyopathy, diabetes and scoliosis add to the picture, and the genetic test looks for a GAA expansion in the FXN gene.
Which paraneoplastic antibodies are linked to cerebellar ataxia?
Anti-Yo antibodies are linked to ovarian or breast cancer in women, anti-Hu to small cell lung cancer, and anti-Tr to Hodgkin disease, all causing cerebellar degeneration. Their detection should prompt a search for the underlying tumour, even before it is visible on imaging.
Why is alcohol-related ataxia worse in the trunk and legs?
Alcohol-related cerebellar degeneration mainly affects the anterior vermis, which controls the trunk and legs, so gait and truncal ataxia predominate over limb incoordination. Thiamine deficiency coexists in many patients, and abstinence with nutritional support can improve gait over time.