Chapter 21 Ataxia, Dizziness, and Vertigo
ETIOLOGY
What Is Ataxia?
Ataxia is the lack of control over coordinated muscular movement, including posture, eye movements, limb movements, and speech. Because of the systemic nature of most etiologies of ataxia in childhood, anatomic localization is not as useful as it is in diseases of the cerebral hemispheres. Acute ataxia occurs after a variety of infections, intoxications, and trauma. It can also be caused by tumors, migraines, inborn errors of metabolism, and other vascular disorders. Chronic ataxia is caused by tumors, hereditary conditions, congenital malformations of the posterior fossa, and inborn errors of metabolism.
What Is Dizziness?
Dizziness is a nonspecific term that usually refers to a sense of lightheadedness and unsteadiness. It is often part of the presyncopal phenomenon (see Syncope, Chapter 39) but can be caused by dehydration, hypotension, anemia, or hypoglycemia. Dizziness should be distinguished from vertigo, ataxia, and weakness. Dizziness may be seen in some dysautonomias. Cardiac causes of dizziness include arrhythmias and postural orthostatic tachycardia syndrome.
How Is Vertigo Different from Ataxia and Dizziness?
Vertigo is usually caused by a vestibular or brainstem disorder. Patients often cannot maintain a stable posture because of a sensation of motion. The differential diagnosis includes labyrinthitis, medication (e.g., aminoglycosides), migraine, seizures, motion sickness, or brainstem stroke.
EVALUATION
What History Helps in Diagnosis of Ataxia?
Most causes of ataxia can be differentiated from one another with a thorough history and physical examination. You must identify the time course (acute vs. chronic), anatomic localization (cerebellar vs. sensory), and age-related disorders. Family history is critical. It is important to distinguish age-appropriate clumsiness from pathologic ataxia. It is also important to distinguish ataxia from weakness because the causes are different.
How Does Acute Ataxia Present Most Commonly?
Acute cerebellar ataxia of childhood is the most common form of ataxia and is usually seen in toddlers and early-school-aged children. It is a diagnosis of exclusion. Viral infections such as Epstein-Barr virus, varicella, enteroviruses, and others often precede the onset of ataxia. Parents usually describe an abrupt onset: “My child was ‘fine’ until he woke up from a nap.”
What Neurologic Findings Identify the Cause of Ataxia?
The neuroanatomy of balance requires both afferent and efferent pathways. Sensory input is crucial for feedback to motor neurons and planning centers. Diseases that affect the vestibular apparatus (e.g., labyrinthitis) can cause imbalance, as can those that affect motor planning (e.g., cerebellar tumor). When ataxia originates in the cerebellum, clinical features help localize the abnormality: Gait unsteadiness, abnormal speech, or nystagmus point to a midline lesion in the vermis. In contrast, dysmetria, demonstrated by having the child reach for a toy, or hypotonia most likely result from a lesion in the cerebellar hemispheres.
Can Physical Examination Identify the Cause of Ataxia?
Conjunctival or cutaneous telangiectasias are seen in Ataxia-Telangiectasia. Cardiac abnormalities, diabetes, and orthopedic abnormalities, including pes cavus and scoliosis, are seen in Friedreich’s ataxia. Strange odors can be associated with some inborn errors of metabolism. The opsoclonus-myoclonus syndrome (“dancing eyes, dancing feet”) is seen occasionally with an occult neuroblastoma. The presence or absence of reflexes can be critical in distinguishing cerebellar causes from sensory causes of ataxia.
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