🧠 Childhood Ataxia - Viva Questions & Examiner Answers

1. Clinical Anatomy & Functional Organization of Cerebellum

Viva Question / Counter-Question	Model Examiner-Grade Answer
What are the three phylogenetic and functional divisions of the cerebellum, and how do they correspond to clinical signs?	The cerebellum is divided into three distinct functional zones: 1. Archicerebellum (Vestibulocerebellum / Flocculonodular Lobe): Connected with vestibular nuclei via inferior cerebellar peduncle. Controls balance, equilibrium, and vestibulo-ocular reflexes. Lesions cause: Nystagmus, vertigo, loss of equilibrium, dysequilibrium without limb dysmetria. 2. Paleocerebellum (Spinocerebellum / Vermis & Paravermal Cortex): Connected with spinocerebellar tracts. Coordinates axial/truncal posture and locomotion. Lesions cause: Truncal ataxia, titubation of head/trunk, wide-based staggering gait, scanning dysarthric speech. 3. Neocerebellum (Pontocerebellum / Cerebrocerebellum / Lateral Hemispheres): Connected with contralateral cerebral cortex via pontine nuclei. Controls voluntary, smooth planning and fine coordination of ipsilateral extremities. Lesions cause: Appendicular dysmetria, intention tremor, dysdiadochokinesia, Holmes rebound phenomenon. VIVA TRAP: Cerebellar hemisphere lesions manifest on the ipsilateral side of the body because the efferent pathway crosses twice (Superior cerebellar peduncle crosses at midbrain decussation $\rightarrow$ Thalamus $\rightarrow$ Motor cortex $\rightarrow$ Corticospinal tract crosses again at medullary pyramids).
Counter-Question: Name the four deep cerebellar nuclei from lateral to medial.	From lateral to medial: Dentate, Emboliform, Globose, and Fastigial nuclei (Mnemonic: "Don't Eat Greasy Food"). Emboliform and Globose together form the nucleus interpositus. Fastigial nucleus mediates vestibular/vermal outputs; Interpositus mediates spinocerebellar outputs; Dentate mediates cerebrocerebellar outputs to the VL thalamus.
Counter-Question: Which cerebellar peduncle carries the major output fibers?	The Superior Cerebellar Peduncle (Brachium Conjunctivum) carries the primary efferent pathways (dentatorubrothalamic tract) from the dentate nucleus to the contralateral red nucleus and VL nucleus of the thalamus. The Middle Peduncle (Brachium Pontis) is purely afferent (corticopontocerebellar), and the Inferior Peduncle (Restiform body) is mixed (spinocerebellar and vestibulocerebellar afferents).

2. Bedside Differentiation: Cerebellar vs. Sensory vs. Vestibular Ataxia

Viva Question / Counter-Question	Model Examiner-Grade Answer
How do you clinically distinguish Cerebellar Ataxia from Sensory and Vestibular Ataxia at the bedside?	1. Cerebellar Ataxia: • Wide-based, staggering, titubating gait; unsteadiness present with eyes open and unchanged/minimally worse with eyes closed. • Associated with dysmetria, intention tremor, dysdiadochokinesia, pendular reflexes, and scanning speech. • Romberg's test is Negative (patient is unsteady even with eyes open). 2. Sensory Ataxia (Dorsal Column / Proprioceptive Loss): • High-steppage, stomping gait (patient watches their feet to compensate visually). • Worsens dramatically in the dark or when washing the face with eyes closed. • Loss of joint position and vibration sense; normal speech and no intention tremor. • Romberg's test is Positive (stands steadily with eyes open, but immediately sways or falls upon closing eyes). 3. Vestibular Ataxia: • Past-pointing and falling directed towards the side of the hypofunctioning labyrinth. • Prominent true rotatory vertigo, nausea, vomiting, tinnitus, and unidirectional horizontal-rotatory nystagmus (fast phase away from the lesion). • No appendicular dysmetria or dysarthria.
Counter-Question: Why is it incorrect to state "Romberg test was positive" in a patient with acute cerebellar ataxia?	VIVA TRAP: Romberg's test evaluates proprioception (dorsal columns), NOT cerebellar integrity. A patient must first be able to stand steadily with feet together and eyes open. In severe cerebellar ataxia, the patient is unsteady and sways with eyes open; hence the test cannot be properly performed and is Negative / Invalid. Romberg is positive only when the patient is stable with eyes open and loses balance specifically upon closing eyes.
Counter-Question: What is Frontal Ataxia (Bruns ataxia)?	Ataxia caused by frontal lobe lesions (tumors, normal pressure hydrocephalus) affecting the frontopontocerebellar pathways. Characterized by gait apraxia / magnetic gait (feet glued to the floor, hesitation in initiating steps, preserved coordination on bed examination).

3. Acute Ataxia in Children: Etiology & Clinical Approach

Viva Question / Counter-Question	Model Examiner-Grade Answer
What is the most common cause of acute ataxia in children, and what is its clinical profile?	Acute Post-Infectious Cerebellar Ataxia (APCA) accounts for $30-50\%$ of all acute ataxia presentations in childhood. • Peak Age: 2 to 6 years. • Trigger: 1 to 3 weeks following a viral prodrome, most classically Varicella-Zoster Virus (VZV) ($>25\%$), followed by EBV, Enteroviruses, Measles, Mumps, Influenza, or Parvovirus B19. • Onset: Sudden or over 24–48 hours. • Clinical Manifestations: Severe pancerebellar ataxia (titubation, staggering gait, dysmetria, intention tremor, horizontal nystagmus, scanning dysarthria) in an otherwise conscious, playful child. • Key Negatives: Normal sensorium, no pyramidal weakness, flexor plantars, no fever at onset of ataxia, no meningeal signs. • Prognosis: Self-limiting; $85-90\%$ recover completely within 2–8 weeks without residual sequelae.
Counter-Question: What is the pathogenesis of post-varicella APCA? Is Acyclovir indicated?	Pathogenesis is immune-mediated post-infectious demyelination and molecular mimicry between viral epitopes and Purkinje cell antigens (intrathecal autoantibody generation), rather than direct viral invasion of cerebellar parenchyma. VIVA TRAP: Acyclovir is NOT indicated in classic post-varicella APCA presenting 1–2 weeks after rash crusted, because active viral replication has ceased. Management is conservative/supportive. Oral or IV steroids are considered only in unusually severe, prolonged, or ADEM-overlapping cases.
Counter-Question: How do you differentiate APCA from Acute Disseminated Encephalomyelitis (ADEM)?	• APCA: Pure, isolated cerebellar involvement; sensorium is clear/normal; no seizures; plantars are flexor; MRI is normal in $>70\%$ or shows subtle isolated cerebellar cortex changes. • ADEM: Multifocal CNS demyelination; prominent encephalopathy (lethargy, irritability, stupor), seizures, pyramidal signs (spasticity, hyperreflexia, extensor plantars), cranial neuropathies, and asymmetric white matter hyperintensities across cerebral subcortical white matter, thalami, and spinal cord on MRI.

4. Episodic & Intermittent Ataxias

Viva Question / Counter-Question

Model Examiner-Grade Answer

What are the major categories and causes of episodic/intermittent ataxia in children?

1. Episodic Ataxias (Channelopathies):
• EA-1: KCNA1 gene (potassium channel); brief episodes (seconds to minutes) triggered by startle/exercise; associated with continuous interictal myokymia.
• EA-2: CACNA1A gene (P/Q-type calcium channel); longer episodes (hours to days) triggered by stress, fever, alcohol; responsive to Acetazolamide.
2. Inborn Errors of Metabolism:
• Urea Cycle Disorders (OTC deficiency), Maple Syrup Urine Disease (MSUD), Hartnup disease, Pyruvate dehydrogenase deficiency. Episodic ataxia provoked by fever, fasting, or high-protein meals; associated with hyperammonemia/acidosis.
3. Basilar Artery / Vestibular Migraine:
• Vertigo, ataxia, visual aura, occipital headache, family history of migraine.
4. Epileptic Ataxia:
• Non-convulsive status epilepticus or postictal state.

Counter-Question: What is Hartnup disease and what is its characteristic clinical triad?

An autosomal recessive defect in the SLC6A19 neutral amino acid transporter in intestinal mucosa and renal tubules, leading to impaired tryptophan absorption and pellagra-like niacin deficiency.
• Triad: (1) Intermittent cerebellar ataxia, (2) Photosensitive pellagra-like dermatitis, (3) Emotional instability / psychosis.
• Diagnostic Hall-mark: Neutral aminoaciduria.
• Treatment: High-protein diet + Oral Nicotinamide ($50-300\text{ mg/day}$).

5. Chronic Progressive Ataxia: Friedreich Ataxia & Ataxia-Telangiectasia

Viva Question / Counter-Question	Model Examiner-Grade Answer
What is the genetic and clinical hallmark of Friedreich's Ataxia (FA)?	• Genetics: Autosomal recessive, caused by unstable GAA trinucleotide repeat expansion in intron 1 of the FXN gene on chromosome 9q21.1, encoding the mitochondrial protein Frataxin. Normal repeats $<33$; FA patients have $66-1700$ repeats. Frataxin deficiency leads to iron accumulation in mitochondria, oxidative stress, and energy failure. • Pathology: Degeneration of dorsal root ganglia, dorsal spinocerebellar tracts, corticospinal tracts, and posterior columns (fasciculus gracilis/cuneatus). • Clinical Triad: (1) Progressive gait and limb ataxia before age 25, (2) Absent deep tendon reflexes in lower limbs, (3) Bilateral extensor plantar responses. • Associated Features: Pes cavus, hammer toes, kyphoscoliosis, Hypertrophic Cardiomyopathy (HOCM) (leading cause of death in $60\%$), and Diabetes Mellitus ($10-20\%$).
Counter-Question: Why are deep tendon reflexes absent while plantars are extensor in Friedreich's Ataxia?	VIVA TRAP: This apparent contradiction is due to dual-level pathology: 1. Absent DTRs: Due to large-fiber sensory peripheral neuropathy and degeneration of the primary afferent Ia fibers in dorsal root ganglia, interrupting the stretch reflex arc. 2. Extensor Plantars: Due to concomitant corticospinal (pyramidal) tract degeneration above the motor neuron level.
Counter-Question: What is Ataxia-Telangiectasia (Louis-Bar Syndrome) and its cardinal features?	Autosomal recessive defect in the ATM gene (11q22.3), responsible for DNA double-strand break repair. • Cardinal Features: 1. Progressive cerebellar ataxia (onset at $1-3$ years). 2. Oculocutaneous telangiectasia (appears at $3-6$ years on bulbar conjunctiva, pinna, neck). 3. Oculomotor apraxia (difficulty initiating saccades; head thrusting). 4. Combined Immunodeficiency: Low serum $\text{IgA}$, $\text{IgE}$, and $\text{IgG}_2$, causing recurrent sinopulmonary infections and bronchiectasis. 5. Malignancy Risk: $100\times$ increased risk of lymphomas, leukemias, and epithelial cancers. 6. Diagnostic Biomarker: Markedly elevated Serum Alpha-Fetoprotein (AFP) ($>95\%$ of cases). • Caution: Extreme radiosensitivity (strictly avoid conventional X-rays/radiation therapy).
Counter-Question: What is Ataxia with Vitamin E Deficiency (AVED)?	Autosomal recessive mutation in the TTPA gene (8q13) encoding $\alpha$-tocopherol transfer protein. Clinically identical phenotype to Friedreich ataxia (progressive ataxia, absent reflexes, extensor plantars, retinitis pigmentosa), but frataxin genetics are normal and serum Vitamin E is undetectable. Curable / Arrestable with lifelong high-dose Vitamin E ($40-50\text{ mg/kg/day}$).

6. Opsoclonus-Myoclonus-Ataxia Syndrome (OMAS / Kinsbourne Syndrome)

Viva Question / Counter-Question

Model Examiner-Grade Answer

What is Opsoclonus-Myoclonus-Ataxia Syndrome (OMAS) and why is it considered an oncological emergency?

OMAS (Kinsbourne syndrome / "Dancing Eyes, Dancing Feet") is an immune-mediated paraneoplastic or parainfectious encephalopathy characterized by:
1. Opsoclonus: Rapid, involuntary, chaotic, non-rhythmic, multidirectional conjugate saccadic eye movements persisting during sleep.
2. Myoclonus: Multifocal, lightning-fast jerks of limbs, trunk, and face.
3. Severe Ataxia: Inability to sit, stand, or walk.
4. Extreme Irritability & Sleep Disturbances.

VIVA TRAP: In $50\%$ of pediatric cases, OMAS is a paraneoplastic manifestation of an occult Neuroblastoma (or ganglioneuroblastoma). A thorough search for neuroblastoma must be instituted immediately.

Counter-Question: What is the diagnostic evaluation and treatment protocol for OMAS?

• Investigation Protocol:
1. MRI of Chest, Abdomen, and Pelvis (or dedicated CT) to locate paravertebral/adrenal neuroblastoma.
2. 24-hour urinary catecholamines (VMA and HVA).
3. Whole-body $^{123}\text{I-MIBG}$ scintigraphy.
4. CSF analysis (oligoclonal bands, neuronal autoantibodies).
• Treatment Protocol:
1. Surgical excision of neuroblastoma if present.
2. Immunomodulation (Triple Therapy): High-dose IV Methylprednisolone or ACTH + IVIG ($2\text{ g/kg}$) + Rituximab (anti-CD20) or Cyclophosphamide for severe/refractory disease.

7. Cerebellar Signs, Clinical Maneuvers & Pathophysiology

Viva Question / Counter-Question	Model Examiner-Grade Answer
Explain the pathophysiology of the Stewart-Holmes Rebound Phenomenon.	When a patient flexes their elbow against examiner resistance and the resistance is suddenly released, a healthy cerebellum rapidly activates the antagonist muscle (triceps) to brake the movement. In cerebellar lesions, loss of cerebellar motor prediction and decreased reciprocal antagonist tone causes delayed braking, resulting in an unchecked, exaggerated rebound swing that may hit the patient's own chest/face (Positive Stewart-Holmes sign).
Counter-Question: What causes the Pendular Knee Jerk in cerebellar disease?	Normal patellar reflex is checked after 1–2 oscillations due to normal muscle spindle and antagonist hamstring tone. In cerebellar lesions, hypotonia and defective damping by antagonist muscles allows the dangling lower leg to swing back and forth repeatedly like a pendulum ($>4$ oscillations) before coming to rest.
Counter-Question: What is the anatomical basis of Scanning / Ataxic Speech?	Scanning speech is caused by asynergia and incoordination of the respiratory, laryngeal, and articulatory muscles due to lesions in the cerebellar vermis/paravermis. Words are segmented into individual syllables with unnatural pauses, irregular volume bursts, and abnormal pitch modulation.
Counter-Question: What clinical scale is used to objectively quantify cerebellar ataxia?	The SARA (Scale for the Assessment and Rating of Ataxia) score, comprising 8 items: (1) Gait, (2) Stance, (3) Sitting, (4) Speech disturbance, (5) Finger chase, (6) Nose-finger test, (7) Fast alternating hand movements, (8) Heel-shin slide. Total score ranges from $0$ (no ataxia) to $40$ (most severe ataxia).