This study examines the concept of neurasthenia in a longitudinal cohort of young adults selected from a community sample of the canton of Zurich, Switzerland. The major focus is on the validity of the case definition of neurasthenia. Close approximations of the proposed descriptive and research definitions of the ICD-10 are employed as well as the concept of ‘irritable weakness' as described in 1831 by Kraus (1926-1932). The prevalence of neurasthenia defined according to the ICD-10 criteria was: 1% across 10 years and 0·9% in 1988 for a duration criterion of ≥ 3 months; and 8·1% across 10 years and 12% in 1988 for a duration criterion of ≥ 1 month. The duration criterion of ≥ 3 months appeared to be excessively restrictive to represent individuals with neurasthenia in the community. Subjects with 1 month episodes of neurasthenia exhibited sufficient differences from controls and similarities to subjects with anxiety or depressive disorders to justify a 1 month duration criterion for neurasthenia in community samples. The clinical significance of neurasthenia was indicated by the magnitude of subjective distress, and occupational and social impairment reported by the majority of the cases. Prospective assessment of the longitudinal course of neurasthenia revealed that approximately 50% of the cases continued to exhibit this disorder at follow-up. Our findings suggest that neurasthenia is equally likely to represent an early manifestation of affective illness as it is a consequence in those neurasthenic subjects who exhibited comorbid affective disorders. The magnitude, chronicity, impairment, longitudinal stability and distinction from anxiety and depression associated with this condition in the general population, suggest that neurasthenia is an important diagnostic entity for which additional validation studies should be undertake
