Ataxia
Ataxia
Ataxia or dystaxia refers to a lack of coordination of voluntary motor acts, impairing their smooth performance. The rate, range, timing, direction, and force of movement may be affected. Ataxia is used most frequently to refer to a cerebellar problem, but sensory ataxia, optic ataxia, and frontal ataxia are also described, so it is probably best to qualify ataxia rather than to use the word in isolation.
- Cerebellar ataxia:
- Defective timing of agonist and antagonist muscle contraction (asynergia) produces jerking, staggering, inaccurate movements (decomposition of movement), which may manifest as intention tremor, dysmetria (past pointing), dysdiadochokinesia, ataxic dysarthria (sometimes known as scanning speech, although this also has other connotations), excessive rebound phenomenon, macrographia, head tremor (titubation), gait ataxia, and abnormal eye movements (nystagmus, square-wave jerks, saccadic intrusions). There may be concurrent limb hypotonia. Cerebellar hemisphere lesions cause ipsilateral limb ataxia (hemiataxia; ataxia on finger-nose and/or heel-shin testing) whereas midline cere- bellar lesions involving the vermis produce selective truncal and gait ataxia.
- Sensory ataxia:
- Results from impaired proprioception, and may be seen in disease of the dorsal (posterior) columns of the spinal cord (hence "spinal ataxia"), sensory neuropathies, and neuronopathies affecting the dorsal root ganglia. It is markedly exacerbated by removal of visual cues (e.g., as in Romberg’s sign), unlike the situation with cerebellar ataxia, and may also lead to pseudoathetosis.
- Optic ataxia:
- Misreaching for visually presented targets, with dysmetria, due to a parieto-occipital lesion, as seen in Balint’s syndrome.
- "Frontal ataxia":
- Similar to, and sometimes indistinguishable from, cerebellar ataxia, but results from lesions of the contralateral frontal cortex or frontopontine fibers, often from tumors invading the frontal lobe or corpus callosum. These fibers run in the corticopontocerebellar tract, synapsing in the pons before passing through the middle cerebellar peduncle to the contralateral cerebellar hemisphere.
Triple ataxia, the rare concurrence of cerebellar, sensory and optic types of ataxia, may be associated with an alien limb phenomenon (sensory type).
There are many causes of cerebellar ataxia, including:
- Similar to, and sometimes indistinguishable from, cerebellar ataxia, but results from lesions of the contralateral frontal cortex or frontopontine fibers, often from tumors invading the frontal lobe or corpus callosum. These fibers run in the corticopontocerebellar tract, synapsing in the pons before passing through the middle cerebellar peduncle to the contralateral cerebellar hemisphere.
- Inherited:
- Autosomal recessive: Friedreich’s ataxia
Autosomal dominant: clinically ADCA types I, II, and III, now reclassified genetically as spinocerebellar ataxias, types 1-25 now described
Episodic ataxias: channelopathies involving potassium (type 1) and calcium (type 2) channels
Mitochondrial disorders Huntington’s disease
Dentatorubropallidoluysian atrophy (DRPLA)
Inherited prion diseases, especially Gerstmann-Straussler- Scheinker (GSS) syndrome
- Autosomal recessive: Friedreich’s ataxia
- Acquired:
- Cerebrovascular events (infarct, hemorrhage): usually cause hemiataxia; postanoxic cerebellar ataxia
Inflammatory: demyelination: multiple sclerosis, Miller Fisher variant of Guillain-Barré syndrome, central pontine myelinolysis Inflammatory: infection: cerebellitis with Epstein-Barr virus; encephalitis with Mycoplasma; HIV
Neoplasia: tumors, paraneoplastic syndromes Neurodegeneration: one variant of multiple system atrophy (MSA-C); prion diseases (Brownell-Oppenheimer variant of sporadic Creutzfeldt-Jakob disease, kuru); idiopathic late- onset cerebellar ataxia
Drugs/toxins: for example, alcohol, phenytoin
Metabolic: vitamin E deficiency, thiamine deficiency (Wernicke’s encephalopathy), gluten ataxia, hypothyroidism (debatable)
- Cerebrovascular events (infarct, hemorrhage): usually cause hemiataxia; postanoxic cerebellar ataxia
References
Klockgether T (ed.). Handbook of ataxia disorders. New York: Marcel Dekker, 2000
Wood NW, Harding AE. Ataxic disorders. In: Bradley WG, Daroff RB, Fenichel GM, Marsden CD (eds.). Neurology in clinical practice: principles of diagnosis and management (3rd edition). Boston: Butterworth-Heinemann, 2000 309-317
Cross References
Alien hand, Alien limb; Asynergia; Balint’s syndrome; Cerebellar syndromes; Dysarthria; Dysdiadochokinesia; Dysmetria; Head tremor; Hemiataxia; Hypotonia, Hypotonus; Macrographia; Nystagmus; Optic ataxia; Proprioception; Pseudoathetosis; Rebound phenomenon; Rombergism, Romberg’s sign; Saccadic intrusion, Saccadic pursuit; Scanning speech; Square-wave jerks; Tandem walking; Tremor
