[Apathy in the structure of mental and neurological disorders of the old age].
The studies on apathy, a common phenomenon in psychiatry, are summarized. The definitions of this term suggested by different authors are presented. The difference between apathy as a symptom and apathy as a syndrome is described. Main pathogenetic mechanisms of the development and epidemiology of this disorder, the results on the differential diagnosis of apathy and depression in patients with neurological and mental diseases as well as methods of treatment are presented.