‘Whether or not it is worthwhile to distinguish between “neurasthenia” and “dysthymic disorders” must depend either on the demonstration that such syndromes have different social covariates, or pursue a different course, or have particular responses to treatment. Until such studies are forthcoming, the distinction seems especially insubstantial.’ (Goldberg & Bridges, 1991)

Epidemiological studies now indicate that fatigue is one of the most common symptoms of ill-health in the community, primary care and other medical settings, and that syndromal diagnoses based on fatigue (including chronic fatigue and neurasthenia) are prevalent and major sources of health care utilization. Such syndromes are characterized by a combination of persistent and disabling fatigue and neuropsychological and neuromuscular symptoms (Lloyd et al. 1990; Angst & Koch, 1991; Sharpe et al. 1991; Fukuda et al. 1994). Essentially, the differences between these syndromes reflect variations in duration criteria rather than symptom constructs. Specifically, the Centers for Disease Control (CDC) defines ‘prolonged fatigue’ as a syndrome of at least 1 month's duration, and chronic fatigue (including idiopathic and chronic fatigue syndrome – CFS) as a fatigue syndrome of at least 6 months duration (Fukuda et al. 1994). The ICD-10 classification system (World Health Organization, 1992) now includes a formal diagnosis of neurasthenia (F48.0) based on mental and physical fatigue of at least 3 months duration. Despite the current international and epidemiological interest in these disorders, DSM-IV has simply included them within the ‘Undifferentiated Somatoform Disorders – 300.81’ category (American Psychiatric Association, 1994).