SUBTHRESHOLD DEPRESSIONS - CLINICAL AND POLYSOMNOGRAPHIC VALIDATION OF DYSTHYMIC, RESIDUAL AND MASKED FORMS

We summarize clinical and polysomnographic findings in support of the existence of a broad and prevalent spectrum of less than syndromal or subthreshold depressive conditions that constitute subaffective disord ers. Many of these conditions were previously subsumed under such rubr ics as 'neurotic,' 'characterological,' and 'existential' depressions. Prospective follow-up studies of neurotic depressions (defined by a p redominance of the psychological features of, in most instances, less. than syndromal depression) have demonstrated their transformation int o moderate to melancholic or psychotic depressive, and even bipolar, d isorders. Many characterological depressives (outpatients with early i nsidious onset and fluctuating chronicity of subthreshold manifestatio ns falling short of full syndromal depression), were shown to have sho rtened REM latency, increased REM%, redistribution of REM to the first part of the night, lassie diurnality, high rates of family history fo r mood disorders, positive response to antidepressants and sleep depri vation, and prospective follow-up course leading to major affective ep isodes. Shortened REM latency and related sleep neurophysiological dis turbances have also been reported to characterize so-called 'borderlin e' personality disorder even when examined in the absence of concomita nt major depression. Finally, among primary care referrals to a sleep disorders center, short REM latency was found in a large number of pat ients without subjective mood change but with somatic manifestations o f depression (meeting Probable Feighner Depression and/or lesser subac ute manifestations). Rather than being incidental, the REM disturbance s in the foregoing studies appear consistently on consecutive nights o f polysomnography in the subthreshold affective group; this was not th e case for patients with non-affective personality and anxiety disorde rs. The findings overall tend to support a common neurophysiological s ubstrate for subthreshold and melancholic depressions and, interpreted in the context of clinical observations, family history and follow-up course, uphold the validity of dysthymic, intermittent and subsydroma l depressions. (C) 1997 Elsevier Science Ireland B.V.