CHAPTER 15 ■ ACUTE ATAXIA JACLYN N KLINE, LUCA BARTOLINI INTRODUCTION Ataxia is defined as impaired coordination of voluntary movements, usually caused in children by cerebellar dysfunction or, less frequently, vestibular or proprioceptive afferent dysfunction While uncommon, acute ataxia in children is important to recognize, because an early diagnosis may have significant therapeutic implications Ataxia is usually associated with other signs of neurologic dysfunction, and the three most common causes of acute ataxia in children are: (1) Acute postinfectious cerebellar ataxia, (2) Drug ingestion, and (3) Guillain–Barré syndrome (GBS) and its variants (Table 15.1 ) HOW TO DIAGNOSE ATAXIA ON NEUROLOGIC EXAMINATION Ataxia can manifest as abnormal timing of contraction of agonist/antagonist muscles (dysrhythmia) and abnormal movement trajectory, resulting in frequent overshooting and overcorrecting (dysmetria) Symptoms and signs often relate to the anatomic location of the cerebellum that is affected by the underlying process Gait and truncal ataxia are observed in diffuse processes and those involving the cerebellar vermis Gait ataxia is the most common presentation and consists of a wide-based gait with inability to walk without support, especially on tandem gait When the deficit is more evident with the eyes closed, sensory or vestibular causes should be considered Young children may just refuse to ambulate Lesions in the cerebellar hemispheres or peduncles are associated with ipsilateral limb ataxia Appendicular ataxia, caused by lesions in the lateral hemispheres of the cerebellum that leads to ataxic movements in the extremities, can be unmasked by performing the rapid alternating movement, finger tapping, and finger-to-nose tests, especially if the examiner’s finger is held at the extreme of the patient’s reach and moved unpredictably Similarly, heel-to-shin test can be done for the lower extremities, but generally requires more cooperation and is rarely feasible in younger patients Overshoot can also be observed when the patient is asked to suddenly raise his outstretched arms from their lap to the level of the examiner’s hand This also allows detection of postural tremor, which is also a cerebellar sign Examination can be affected by the presence of upper or