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Introduction
Ataxia (Greek 'taxis' = order 1 ) refers to incoordination without significant weakness. It may result from cerebellar, vestibular or sensory (proprioceptive) dysfunction. The presenting features include impaired balance and/or directional limb movements and/or dysarthria, depending upon the underlying locus of pathology. There is often clinical confusion between sensory ataxia and cerebellar ataxia 1 2 ; patients with chronic sensory ataxia may carry the wrong diagnostic label for decades. There are many possible causes which need a careful history, examination and appropriately targeted investigations to delineate. We present a clinical algorithm to facilitate this.
Clinical approach
Box 1 Proposed criteria for diagnosing clinically probable sensory ataxia Ataxia confirmed by clinical examination: finger-nose incoordination and/or heel-toe ataxia and/or broad-based ataxic gait
Two or more of: Romberg's sign or ataxia significantly worse with eyes closed, or history of 'wash basin sign' 3
Pseudoathetosis and/or impaired joint position and/or vibration sense/s.
Absence of nystagmus and/or cerebellar dysarthria.
Table 1 lists the characteristics which help to distinguish pure sensory from cerebellar ataxia. 1 2 The degree of impaired joint position or vibration sense loss may vary; patients need a detailed and experienced sensory evaluation to record large fibre sensory deficit. Additionally, distal deep tendon reflexes may be retained in posterior column or non-length-dependent dorsal root ganglion pathologies. Varying degrees of worsened limb or gait ataxia on eye closure is not totally specific for sensory ataxia. Similarly, Romberg's sign may be difficult to perform or interpret in a grossly ataxic patient with a cerebellar disorder. A significant worsening of unsteadiness with visual deprivation (including incoordination of limbs or of station ie, Romberg's sign) requires experienced and focused clinical judgement. We recommend caution in presuming a cerebellar basis for ataxia in the absence of nystagmus and/or dysarthria. Additionally, some 'sensory ataxia-plus' syndromes may have a component of cerebellar ataxia. Distinguishing sensory from cerebellar ataxia is often more difficult than table 1 might imply (see case 2, box 3 ).
Table 1
Sensory ataxia | Cerebellar ataxia |
|
Nystagmus | Absent* | Present |
Dysarthria | Absent* | Scanning/staccato speech |
Eye movements | Sometimes abnormal (eg, CANOMAD) | Normal/slow |
Finger-nose ataxia | Present (significantly worse with eye closure) | Present |
Heel-shin ataxia | Present (significantly worse with eye closure) | Present |
Deep tendon reflexes | Absent/present | Normal/pendular |
Joint position sense | Impaired | Normal |
Pseudoathetosis | Usually present |