309-316 Ryan

Acute childhood ataxia is a common cause of presentation to the pediatric emergency room or child neurologist. The primary concern on initial assessment is to exclude serious causes of this clinical syndrome, including central nervous system infections and mass lesions, while recognizing the essentially benign nature of acute ataxia in most children. Childhood ataxia can be diagnostically approached by consideration of the temporal course and presence or absence of associated neurologic abnormalities. In all forms of childhood ataxia, outcome is largely determined by etiology. In this review, the various causes and syndromes of acute ataxia in childhood are described, with discussion of diagnostic considerations and an approach to investigation, treatment, and prognosis. (J Child Neurol 2003;18:309–316). Received Dec 26, 2002. Received revised Jan 21, 2003. Accepted for publication Jan 21, 2003. From the Department of Neurology (Drs Ryan and Engle), Children’s Hospital Boston, Boston, MA. Presented in part at the Michael J. Bresnan Child Neurology Course, Children’s Hospital, Harvard Medical School, Boston, September 26, 2002. Address correspondence to Dr Monique M. Ryan, Department of Neurology, Fegan 11, Children’s Hospital Boston, 300 Longwood Avenue, Boston MA 02115. Tel: 617-355-2067; fax: 617-264-9691; e-mail: [email protected]. general, the physical examination can be difficult as significantly ataxic children are often hesitant and irritable, necessitating prolonged observation to differentiate poor coordination from weakness. The mental state is important. Children with postinfectious cerebellar ataxia are normally alert and interactive. Abruptly altered responsiveness suggests an ingestion, acute disseminated encephalomyelitis, or stroke. Extreme irritability and decreased speech output can be seen in the opsoclonus-myoclonus syndrome. Nystagmus is common to disorders affecting the cerebellar hemispheres. Additional abnormalities of cranial nerve examination, such as papilledema and cranial nerve palsies, suggest an intracranial focal lesion or hydrocephalus. Pupillary abnormalities can be seen with mass lesions, raised intracranial pressure, stroke, or intoxication. Asymmetries of limb tone, power, and the deep tendon reflexes are uncommon in acute cerebellar ataxia and should prompt consideration of other conditions. Truncal ataxia is easier to appreciate when the child sits unsupported. ETIOLOGY OF ACUTE ATAXIA IN CHILDHOOD Cerebellar Disorders Acute ataxia secondary to cerebellar dysfunction is characterized by hypotonia, gait abnormalities (wide based, lurching, possibly staggering), poor maintenance of truncal position (titubation), and speech abnormalities (fluctuations in clarity, rhythm, tone, and volume). Poor coordination of voluntary movements (dysmetria) results in nystagmus, underor overshooting of limb movements (best seen on finger-nose or toe-target testing), and difficulty with rapid alternating movements (dysdiadochokinesia), which may be associated with intention tremor (which is oscillatory, to and fro in a plane perpendicular to the object being approached). The deep tendon reflexes can be pendular, with slowed contraction and relaxation phases, although this is often difficult to appreciate. Some clue to localization of the lesion within the cerebellum can be apparent on examination: vermal (midline) lesions cause dysarthria, truncal titubation, and gait abnormalities, whereas lesions of the cerebellar hemispheres spare speech but result in ipsilateral limb hypotonia, dysmetria, and tremor. When walking, patients tend to veer in the direction of the affected cerebellar hemisphere. Lesions of the deep cerebellar nuclei cause resting tremor, myoclonus of the extremities and palate, and opsoclonus. Findings in cerebellar ataxia remain unchanged in severity whether the eyes are open or closed. Infectious or Immune Mediated Acute Cerebellar Ataxia The most common cause of childhood ataxia, accounting for about 40% of all cases, is acute cerebellar ataxia.1 Acute cerebellar ataxia usually results from postinfectious cerebellar demyelination, less commonly occurring as a result of direct infection of the cerebellum. Postinfectious cerebellar demyelination is thought to be an autoimmune phenomenon incited by infection or immunization, with subsequent cross-reaction of antibodies against cerebellar epitopes, although specific autoantibodies have only rarely been identified.2 Acute cerebellar ataxia is most common in younger children (2–4 years) but may be seen in older children and adolescents.1,3 Boys are more commonly affected.3 A history of antecedent illness in the 5 to 21 days before presentation is obtained in about 70% of patients. Numerous infectious agents have been implicated in the pathogenesis of this condition (Table 2). As many as 26% of cases are preceded by varicella.3 Rarely, the development of ataxia precedes the eruptive phase of varicella infection.4 The introduction of universal immunization against varicella is likely to render varicella-related cerebellar ataxia uncommon. To date, only one case of acute cerebellar ataxia temporally related to varicella vaccination has been described.5 Although cerebellar ataxia has long been temporally linked to childhood immunizations (most com310 Journal of Child Neurology / Volume 18, Number 5, May 2003 Table 1. Causes of Acute Ataxia in Childhood Infectious/immune-mediated cerebellar disorders Acute cerebellar ataxia* Acute demyelinating encephalomyelitis* Systemic infections Brainstem encephalitis Multiple sclerosis Toxic: alcohol and drug related* Mass lesions Tumors Vascular lesions Abscesses