Stability of the diagnosis of seasonal affective disorder in a long-term prospective study

Seasonal affective disorder (SAD) is mainly characterized by a seasonal pattern of depressive recurrences over the years. However, few studies have been conducted on the long-term course of patients with SAD, whose findings raised questions about the diagnosis stability over time. This study aimed to better characterize the diagnosis evolution, and determine prognosis markers.

An initial cohort of 225 outpatients diagnosed as having a SAD, was assessed at baseline (T1) for clinical symptoms and response to bright light therapy. One hundred and nineteen patients (53%) were interviewed 2-12 years after (T2).

Of 119 patients reached at follow-up (T2), only 32 patients (27%) still fulfilled the DSM-IV criteria for a stable SAD (S-SAD). A large proportion (59%) of the follow up cohort was in remission and 14% still suffered from a non-seasonal mood disorder. Family history of depression, previous suicide attempt, carbohydrate craving and HAD-depression score at baseline were associated with a stable SAD (S-SAD) diagnosis at T2, the HAD-depression score being the only one still significantly predictive (p=0.025) of a later stable SAD, with a multivariate approach. Carbohydrate craving, a core symptom of SAD, showed a trend (p=0.100) to predict diagnosis stability.

Only 53% patients from the initial cohort were assessed at follow-up.

Patients with eventual stable SAD show more subjective severity (higher HAD-Depression score) and carbohydrate craving at baseline. A low predictive validity of diagnosis criteria suggests that SAD is a temporary expression of a mood disorder rather than a specific disorder.