Idiopathic cerebellar ataxia; IDCA
Definition and Characteristics
The sporadic ataxias are a heterogeneous group of adult-onset ataxia disorders that have a defined acquired cause (acquired or symptomatic sporadic ataxias) or occur without a discernible cause (sporadic ataxia of unknown etiology, SAOA) . The latter category has been recently defined and distinguished from multiple system atrophy (MSA). The major categories of acquired ataxias are alcoholic cerebellar degeneration (ACD)  and paraneoplastic cerebellar degeneration (PCD) . Sporadic ataxias are characterized by progressive cerebellar ataxia without major accompanying symptoms. Disease severity and progression rate are variable and partly depend on the underlying cause. In contrast to SAOA, which usually starts insidiously, ACD and PCD may have a subacute onset.
A recent population-based study of SAOA found a prevalence rate of 9.4:100,000. Prevalence rates of ACD and PCD are unknown.
Molecular and Systemic Pathophysiology
The etiology and pathogenesis of SAOA are unknown.
ADC is due to the toxic action of alcohol and its degradation product acetaldehyde on cerebellar Purkinje neurons. In addition, a nutritional deficiency in vitamin B1 (thiamine) strongly contributes to the development of this disorder.
PCD degeneration is an immune-mediated disorder occurring in patients with malignant tumors, mainly small cell lung and breast cancer as well as malignant lymphomas. Many PCD patients have circulating antineuronal antibodies. However, these antibodies do not cause PCD. Instead, PCD is caused by a T-cell-mediated immune attack directed against cerebellar Purkinje neurons.
SAOA is diagnosed by exclusion of MSA and acquired as well as genetic causes of ataxia.
ACD is diagnosed by history and the typical clinical presentation of alcoholic patients.
A definite diagnosis of PCD can only be made by demonstration of an underlying malignant tumor. Screening for antineuronal antibodies alone is not sufficient, since PCD may occur in the absence of antineuronal antibodies.
SAOA is an untreatable condition. As in other ataxias, physiotherapy and speech therapy may be helpful.
A diagnosis of ACD should prompt immediate administration of vitamin B1 (thiamine). Alcohol intake should be completely and lastingly stopped.
In PCD, the underlying tumor should be treated. In most cases, this does not improve ataxia.