Acute ataxia generally has an onset of <24 hours. Drug toxicity and infections are the most common etiologies. Acute metabolic processes, such as hypoglycemia, are also implicated, although they are usually accompanied by multiple systemic manifestations.
In a patient with acute ataxia, the history and physical examination focus on excluding acute infectious etiologies, such as meningitis or encephalitis, recent infections, or immunizations; lesions that result in increased intracranial pressure, such as trauma, hemorrhage, and tumors; and toxic ingestions. Central nervous system infections are usually characterized by fever and headache, and often by mental status changes. The physical examination may reveal neck stiffness. Lesions that cause increased intracranial pressure are associated with headache and vomiting, and the physical examination may reveal papilledema.2,4 In the case of a cerebellar hemorrhage, the onset of ataxia is extremely sudden, whereas with posterior fossa tumors, the history will usually reveal a more protracted process.2 Cerebrovascular disease, such as a stroke, can also result in acute ataxia. This should be considered in those with hypercoagulable states and sickle cell disease.2 Toxic ingestions are likely in patients on antiepileptic medications and are especially common in toddlers. Acute ataxia can also occur after head trauma, in which it can result from a cerebellar hemorrhage or basilar skull fracture.
Any ataxic patient in whom an acute infectious process (meningitis, encephalitis, cerebellar abscess) is considered requires a lumbar puncture. It is imperative that, prior to lumbar puncture, increased intracranial pressure be excluded by computed tomography (CT) scan of the brain.1,2,4 In any case in which ingestion of a toxic substance is suspected, a toxicology screen is indicated. Urine screens are useful for drugs of abuse, whereas serum levels are needed for specific toxins that include antiepileptic medications, lead, carbon monoxide, and alcohol.
Certain causes of acute ataxia are almost unique to the pediatric population and deserve special mention. GBS can present with ataxia, although the associated findings of areflexia and, in the Miller–Fisher variant, ophthalmoplegia distinguish it from acute cerebellar ataxia. Many childhood illnesses and immunizations have been postulated as inciting an autoimmune phenomenon, which can result in acute cerebellar ataxia, ADEM, or brain stem encephalitis.1
A common cause of ataxia in children younger than 6 years is acute cerebellar ataxia. The onset of ataxia is insidious and predominantly affects the gait, although dysmetria, nystagmus, and dysarthria can occur. The affected child is afebrile, and has a normal level of consciousness. Acute cerebellar ataxia is thought to be a postinfectious phenomenon and often occurs 2 weeks after a viral illness. Ataxia has been reported after infection with varicella, influenza, mumps, Epstein–Barr virus, echovirus 6, coxsackie B virus, and other viruses. The gait abnormalities come on abruptly, and are maximum at onset, with the trunk affected more than the extremities.1,6 It is a self-limiting illness with an excellent prognosis, usually resolving in the majority of cases in 2–3 weeks.6 Although therapies such as steroids and intravenous immune globulin have been used, there is really no specific therapy.6 Acute cerebellar ataxia is a diagnosis of exclusion.
Myoclonic Encephalopathy of Infancy (Opsoclonus/Myoclonus)
Myoclonic encephalopathy of infancy (polymyoclonus/opsoclonus) is another cause of acute ataxia. This syndrome occurs in children from 6 months to 3 years of age, in association with occult neuroblastoma.3 It is differentiated from acute cerebellar ataxia by its association with opsoclonus (rapid, chaotic conjugate eye movements), which occur in association with polymyoclonus (severe myoclonic jerks of the limbs and trunk or head).1,3 Irritability and vomiting can also occur. Diagnostic tests that should be initiated in the emergency department (ED) include chest and abdominal CT or MRI, urine vanillylmandelic acid (VMA), and homovanillic acid (HVA).1,3 Treatment for a neuroblastoma should be in consultation with a pediatric oncologist.1,3
Acute Postinfectious Demyelinating Encephalomyelitis
This is a multifocal immune-mediated encephalopathy characterized by ataxia, alteration in level of consciousness, and neurological deficits. Seizures, cranial neuropathies, hemiparesis, sensory deficits, and transverse myelitis are common. These latter findings help distinguish ADEM from acute cerebellar ataxia.2 The patient may have fever, headache, and meningismus. It develops during the recovery from a viral illness, or after vaccination. Repeated episodes of this should prompt a workup for multiple sclerosis.1,2
Up to 60% of childhood brain tumors occur in the brain stem or cerebellum. Those that arise in the posterior fossa often have a slow onset of symptoms including ataxia, headache, and vomiting. However, hydrocephalus from obstruction or a bleed into the tumor can cause abrupt symptoms and decompensation.1,2 The most common tumors of the posterior fossa are cerebellar astrocytoma, brainstem glioma, ependymoma, primitive neuroectodermal tumor, and medulloblastoma.3,7
Guillain–Barré Syndrome/Miller–Fisher Syndrome
This is an acute demyelinating polyradiculoneuropathy that occurs after an infection or immunization. Although it predominantly affects the motor nerves resulting in weakness, 15% of patients develop a loss of sensory input to the cerebellum resulting in a sensory ataxia. The ataxia and weakness is progressive over several days. The Miller–Fisher syndrome is a form of GBS that results in ataxia, areflexia, and ophthalmoplegia. It occurs 5 to 10 days after an infectious illness, especially Campylobacter gastroenteritis.1,2 Diagnostic tests include lumbar puncture looking for cytoalbuminologic dissociation and anti-GQ1b antibody for the Miller–Fisher variant. Patients suspected of these syndromes should be admitted to the hospital for further testing and monitoring as disease progression is variable. Electromyography and nerve conduction studies are helpful to diagnose GBS where specific abnormalities are seen. It is less helpful in diagnosing the Miller–Fisher syndrome, but may demonstrate abnormalities.1
Intermittent or episodic ataxia occurs as acute episodes that are similar in nature. In children, the most common cause of intermittent ataxia is a migraine headache that involves the basilar artery. Besides ataxia, associated symptoms include blurred vision, visual field deficits, vertigo, and headache. In a child experiencing the first basilar migraine, it is essential to exclude an acute infectious process, toxic ingestion, or mass lesion.1
Partial complex seizures can also cause intermittent ataxia but are often associated with alteration of consciousness and possibly characteristic motor manifestations.
Rarely, inborn errors of metabolism result in intermittent ataxia. These include maple syrup urine disease, Hartnup disease, urea cycle defects (citrullinemia, ornithine transcarbamylase deficiency, and argininosuccinic aciduria), multiple carboxylase deficiencies (biotinidase deficiency and isovaleric acidemia), pyruvate decarboxylase and pyruvate dehydrogenase deficiencies.1,8
Patients with intermittent ataxia may not require radiographic or laboratory evaluation in the ED if they present with a known diagnosis. Patients suspected of having seizures are referred for an electroencephalogram (EEG). The rare patient suspected of having an undiagnosed inborn error of metabolism is referred to a pediatric geneticist or endocrinologist.