Ataxia in children: Viva

Branch 1: Localising the lesion

The candidate should confirm that this is a cerebellar ataxia and localise it to the cerebellum rather than to a sensory or a vestibular cause. The acute onset of a wide-based, staggering gait, the slurred speech, and the dysmetria on the finger-to-nose test point to the cerebellum, and the key distinguishing feature is that the gait is present whether the eyes are open or closed, which argues against a sensory ataxia. A strong candidate performs the Romberg test and shows that the gait does not worsen with eye closure, and tests the heel-to-shin movement, the rapid alternating movement for dysdiadochokinesia, and the eye movements for nystagmus, and confirms that the power, tone, reflexes, and sensation are normal, which separates a coordination problem from weakness. [1]

If the examiner presses on the topography, the candidate should explain that a truncal and gait ataxia localises to the midline vermis, which governs posture and balance, while an appendicular ataxia with dysmetria and intention tremor localises to the cerebellar hemisphere on the same side. The teaching point is that the bedside examination alone localises the lesion, and that the pattern of reflex and sensation change, such as the absent reflexes and extensor plantars of Friedreich ataxia, redirects the localisation from a pure cerebellar lesion to a multisystem degeneration. [1]

Branch 2: The imaging decision

If asked whether to image, the candidate should state that neuroimaging is not routine for a child who meets the clinical picture of post-infectious acute cerebellar ataxia. This girl has an acute onset one week after a viral illness, a normal conscious state, a purely cerebellar pattern, and a negative red-flag screen, so she does not need a scan. The candidate should then name the red flags that would change that decision: a headache that is worse in the morning or wakes the child from sleep, effortless early-morning vomiting, papilloedema, a head tilt, a new squint or cranial nerve palsy, a depressed or fluctuating conscious state, a progressive rather than improving course, fever with meningism, and opsoclonus with extreme irritability. [1]

A strong candidate then explains why each red flag matters. The morning headache, the early-morning vomiting, and the papilloedema point to raised intracranial pressure from a posterior fossa tumour obstructing the fourth ventricle, and the head tilt and the cranial nerve palsy point to a brainstem or cerebellar lesion. The systematic review by Wilne and colleagues documented that headache, nausea and vomiting, and gait abnormality are among the commonest features of a childhood central nervous system tumour, and that the interval from symptom onset to diagnosis is often long. The cardinal error is discharging a posterior fossa tumour as a post-infectious ataxia, and the safeguard is the red-flag screen applied to every ataxic child. [3]

Branch 3: Recognising the dangerous mimics

If asked what else it could be, the candidate should run through the dangerous mimics of acute cerebellar ataxia. Drug ingestion is the high-frequency mimic in a toddler with access to medications, and the toxicology history and screen are the diagnostic tools. Central nervous system infection, meningitis or encephalitis, presents with an altered conscious state, fever, and meningism, and demands a lumbar puncture and imaging. Acute disseminated encephalomyelitis presents with encephalopathy and multifocal neurological signs, and cerebellar or brainstem stroke presents with an acute focal deficit. [1]

The candidate should then name the one acute ataxia that every examiner wants to hear: opsoclonus-myoclonus-ataxia syndrome. The child has the chaotic multidirectional saccades of opsoclonus, the dancing eyes, myoclonus, ataxia, and extreme irritability, and around half have an occult neuroblastoma. The candidate should explain that the syndrome is autoimmune or paraneoplastic rather than a self-limiting post-infectious process, that every child is investigated for neuroblastoma with urine catecholamines and imaging, and that the treatment is immunotherapy with corticosteroids, intravenous immunoglobulin, and, for refractory disease, rituximab. The teaching point is that the motor signs may improve while the cognitive and behavioural sequelae persist. [1]

Branch 4: The progressive ataxia

If the examiner shifts to a teenager with a progressive ataxia and absent reflexes, the candidate should diagnose Friedreich ataxia from the constellation. The cardinal combination is a progressive limb and gait ataxia with onset before twenty-five, absent lower limb reflexes, an extensor plantar response, loss of position and vibration sense, pes cavus, scoliosis, and hypertrophic cardiomyopathy. The candidate should explain that the absence of lower limb reflexes with an extensor plantar response and dorsal column loss is the signature that separates Friedreich ataxia from a pure cerebellar lesion, and that the diagnosis is confirmed by the GAA trinucleotide repeat expansion in the FXN gene. [5]

The candidate should then defend the management. The cardiomyopathy is the leading cause of death, so regular cardiology surveillance with echocardiography is essential, and the broader management addresses diabetes, scoliosis, mobility, and the psychosocial impact of a chronic genetic diagnosis. The candidate should confront the omaveloxolone evidence directly: the MOXIe trial showed that omaveloxolone improved the modified Friedreich Ataxia Rating Scale score compared with placebo, and a delayed-start analysis confirmed a durable benefit, making it the first disease-modifying therapy. The goal is a multidisciplinary plan that slows the decline and preserves function and quality of life. [5] [7]