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lower motor neuron signs, since weakness can easily be mistaken for ataxia or the
two signs may coexist. A very useful test that requires little strength to be
performed and can help differentiate weakness from ataxia is done by asking the
patient to follow one of the creases of her thumb with her index finger. Truncal
and appendicular ataxia may coexist in the presence of large lesions or diffuse
processes.
Eye movement abnormalities in cerebellar dysfunction may be more difficult to
detect; nystagmus is often present, and saccades may under- or overshoot the
target. Also, speech can be affected, with irregular changes in volume and rate
(scanning speech).
Ataxia can result from lesions outside of the cerebellum, when the cerebellar
afferent or efferent pathways are disrupted, for example by a lesion in the pons, or
by lesions in the posterior column - medial lemniscal pathway, which result in
positive Romberg sign and loss of joint position sense.

DIFFERENTIAL DIAGNOSIS AND ROLE OF IMAGING AND
LABORATORY TESTS
While several diseases can manifest with ataxia (Table 15.2 ), the most common
cause of acute ataxia in children with normal mental status is acute
postinfectious cerebellar ataxia . This condition is usually observed in toddlers
(60% of patients in large series were aged between 2 and 4 years) and is
characterized by a prodrome of nonspecific viral illness followed after days or up
to 2 to 3 weeks by ataxia. The clinical course is usually benign, with full return to
baseline within 8 months in 70% of children. This remains a clinical diagnosis, as
imaging and CSF analysis are usually unremarkable; sometimes, especially in
younger patients where the examination may not be entirely reliable, brain MRI
and lumbar puncture (LP) should be considered to rule out other causes, such as
acute disseminated encephalomyelitis (ADEM—see below), because of potential
treatment implications.
In a child with ataxia and abnormal mental status , urgent brain imaging (plain
CT head or, ideally, brain MRI if available without significant delay) is

warranted, and LP should be considered. Imaging, particularly MRI, allows the
clinician to rule-out brain tumors, demyelinating conditions, cerebellitis, and
stroke. CSF pleocytosis (>5 cells/mm3) may be observed in different conditions
and while bacterial meningitis is unlikely in an ataxic child without fever or
meningismus, viral meningoencephalitis remains a possibility, especially if the
pleocytosis is primarily lymphocytic.