[Secondary parkinsonian syndromes].

Secondary parkinsonism (SP) is caused by an identified structural, toxic, or metabolic mechanism. The first group of SP syndromes includes disorders caused by a primary pathological process in the brain. The second group includes disorders with a primary extrinsic or ubiquitous causal factor resulting either from reversible dysfunction of the basal ganglia or structural disorders related to the predominant or selective vulnerability to aggression of the basal ganglia. The pathophysiological aspects SP are developed here, particularly vascular syndromes and syndromes secondary to hydrocephalus. In both conditions, it is rare that SP resembles Parkinson's disease. The pathophysiology is poorly understood, but would involve, in most cases, corticostratial and/or thalamocortical connections in the basal ganglia system. For the clinician, the practical problem is frequently to determine whether a patient's parkinsonism can be related to an identifiable cause or whether there is an associated Parkinson's disease or other degenerative disease. When both a known cause of parkinsonism and Parkinson's disease are present, the cause may be asymptomatic, reveal Parkinson's disease, have an aggravating effect on the underlying disease, or modify its clinical expression.