ATAXIA

JANET H. FRIDAY, MD

Acute childhood ataxia is an uncommon presenting complaint in the emergency department. Ataxia is defined as a disturbance in coordination of movements and may be manifested as an unsteady gait. When it occurs, it is a distressing problem to both parent and clinician. It is important to establish the sign because true ataxia may be difficult to differentiate from clumsiness in toddlers. Parents are generally more sensitive to gait abnormalities in this age group. In older children, ataxia may be confused with weakness or vertigo. Life-threatening causes of pure ataxia are rare in children. After consideration of these, the problem may be approached in an orderly, stepwise fashion.

PATHOPHYSIOLOGY

The cerebellum coordinates complex activities such as walking, talking, and eye movements. Ataxia may be caused by either a focal or global pathologic condition within the cerebellum or by disruptions in the afferent or efferent pathways. Anatomically, the cerebellum is located in the posterior cranial fossa, separated from the cerebrum by the tentorium. The ventral borders of the cerebellum form the roof of the fourth ventricle. Space-occupying lesions such as posterior fossa tumors and cerebellar hemorrhage may impede cerebrospinal fluid (CSF) flow, leading to hydrocephalus and increased intracranial pressure (ICP). Conversely, direct pressure on the cerebellar peduncles may cause ataxia.

The cerebellum links with other portions of the central nervous system through the superior, middle, and inferior peduncles via the midbrain, pons, and medulla. Proprioceptive and sensory afferent impulses from muscles, joints, and tendons are carried via inferior peduncles to the cerebellar cortex. Labyrinthine afferent input is also conducted through the inferior peduncles. Connections from frontal motor cortex travel through the middle cerebellar peduncles. The superior peduncles carry efferent output to musculoskeletal tracts from the nuclei of the cerebellum.

The cerebellum is composed of two hemispheres. Because of the decussation patterns, a lesion that affects only one side of the cerebellum will result in movement abnormalities of the ipsilateral side, with distal movements more affected than proximal ones. Midline lesions lead to truncal ataxia, with swaying during standing, sitting, and walking, and/or with titubations (small rhythmic movements) of the head and neck. Finally, the intrinsic function of the cerebellum may be disrupted by toxins and autoimmune and metabolic disorders.

DIFFERENTIAL DIAGNOSIS

Ataxia as a presenting sign invokes a broad differential diagnosis (Table 10.1). Distinguishing among acute, intermittent, and chronic progressive and nonprogressive ataxia may be helpful, although some diagnoses have overlap in their time course at presentation. Fortunately, common causes of pure ataxia (Table 10.2) are not rapidly progressive. Acute cerebellar ataxia or postinfectious cerebellitis is truncal in nature and occurs 8 days to 3 weeks after an infectious illness (see Chapters 102 Infectious Disease Emergencies and 105 Neurologic Emergencies

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