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ADEM is an immune-mediated demyelinating condition, generally monophasic, which often occurs postinfectiously, predominantly in school-age children It is usually associated with focal neurologic deficits, often including ataxia and various degrees of encephalopathy, but also cranial nerve abnormalities, pyramidal signs, and speech impairment Maximal severity is usually observed within to days from onset of symptoms MRI usually shows reversible, ill-defined white matter lesions with frequent involvement of brain (including cortical and subcortical structures such as thalami and basal ganglia) and spinal cord CSF often shows lymphocytic pleocytosis and increased protein Acute cerebellitis is defined as an acute cerebellar syndrome usually in the context of a nonspecific recent infection, accompanied by altered mental status and cerebellar edema on brain imaging TABLE 15.1 COMMON CAUSES OF ACUTE ATAXIA Acute cerebellar ataxia Drug ingestion Guillain–Barré syndrome a a Indicates weakness or vertigo that may mimic ataxia Toxic ingestions (Table 15.3 ) are a common problem in the pediatric population, and should always be considered among other medical etiologies A detailed history including available drugs in the child’s home, or the home of any caregivers, can be critical in making this diagnosis Benzodiazepines cause lethargy, altered mental status, and ataxia Antiepileptic drugs (AEDs), particularly phenytoin and carbamazepine, are also causes of ataxia in the pediatric population Ingestions of these medications can often present with nystagmus with ataxia Dextromethorphan, a primary ingredient in many overthe-counter cough suppressants, is also an important drug to consider in an ataxic patient At lower doses, this can cause euphoria, which leads to its abuse, particularly among adolescents; however, in higher doses it can cause ataxia Ethanol is a common substance of abuse among adolescents, but must also be considered in younger children as ethanol is prevalent in many homes in the form of beverages, cough syrups, and mouthwash and can lead to ataxia from cerebellar dysfunction Marijuana and synthetic cannabinoids are other common substances of abuse that can lead to ataxia along with their myriad of symptoms, and should be considered in a patient presenting with associated tachycardia or mydriasis Testing with urine drug screen, serum ethanol level, and antiepilepsy drug levels, when applicable, should be considered in the workup for ataxia TABLE 15.2 DIFFERENTIAL DIAGNOSIS OF ACUTE OR RECURRENT ATAXIA, INCLUDING LESS COMMON CAUSES Infectious and immune mediated Acute cerebellitis Acute disseminated encephalomyelitis (ADEM) Multiple sclerosis exacerbation Tick paralysis a Meningitis Benign peripheral Benign paroxysmal vertigo a Labyrinthitis a Cerebrovascular Ischemic or hemorrhagic posterior circulation stroke Cerebral sinovenous thrombosis Vasculitis Headache related Migraine Postconcussion syndrome Conversion disorder Genetic/metabolic diseases Hartnup disease Wilson disease Maple syrup urine disease Pyruvate decarboxylase deficiency Episodic ataxia type (paroxysmal ataxia and myokymia) Episodic ataxia type (acetazolamide-responsive ataxia) Posterior fossa pathology Acute hydrocephalus Posterior fossa tumors a Indicates weakness or vertigo that may mimic ataxia TABLE 15.3 DRUGS AND TOXINS THAT MAY CAUSE ATAXIA Benzodiazepines Alcohol Dextromethorphan Marijuana and synthetic cannabinoids Phenytoin Carbamazepine Tricyclic antidepressants Antihistamines Lead 5-Fluorouracil Ethylene glycol Primidone Phenothiazines Topiramate Risperidone Gabapentin Phenobarbital GBS is a postinfectious polyneuropathy with a peak incidence at ages to years that can cause ataxia, and must be considered in a patient presenting with areflexia and weakness, particularly the classic presentation of ascending paralysis and weakness CSF analysis, particularly assessing for elevated protein in the CSF, is key in diagnosing GBS The clinician must also consider Miller Fisher variant, which has more severe and more rapid onset than GBS, and classically presents with ataxia, areflexia, and ophthalmoplegia CSF pleocytosis can also be seen with this illness; however, for definitive testing and diagnosis, neurology consultation should be considered A rare but severe cause for acute ataxia is stroke , either hemorrhagic or ischemic Cerebellar bleeding in children can be associated with arteriovenous malformations or cavernous hemangiomas and often presents with severe headache and signs of increased intracranial pressure (ICP) Posterior circulation