Chronic Fatigue Syndrome (CFS) & seasonal affective disorder: comorbidity, diagnostic overlap, & implications for treatment

This study aimed to determine symptom patterns in patients

with chronic fatigue syndrome (CFS), in summer and winter.

Comparison data for patients with seasonal affective disorder

(SAD) were used to evaluate seasonal variation in mood and

behavior, atypical neurovegetative symptoms characteristic of

SAD, and somatic symptoms characteristic of CFS. Rating scale

questionnaires were mailed to patients previously diagnosed

with CFS. Instruments included the Personal Inventory for

Depression and SAD (PIDS) and the Systematic Assessment for

Treatment Emergent Effects (SAFTEE), which catalogs the

current severity of a wide range of somatic, behavioral, and

affective symptoms.

Data sets from 110 CFS patients matched

across seasons were entered into the analysis. Symptoms that

conform with the Centers for Disease Control and Prevention

(CDC) case definition of CFS were rated as moderate to very

severe during the winter months by varying proportions of

patients (from 43% for lymph node pain or enlargement, to 79%

for muscle, joint, or bone pain). Fatigue was reported by 92%.

Prominent affective symptoms included irritability (55%),

depressed mood (52%), and anxiety (51%). Retrospective monthly

ratings of mood, social activity, energy, sleep duration,

amount eaten, and weight change showed a coherent pattern of

winter worsening. Of patients with consistent summer and

winter ratings (n = 73), 37% showed high global seasonality

scores (GSS) > or = 10. About half this group reported

symptoms indicative of major depressive disorder, which was

strongly associated with high seasonality.


cluster analysis of wintertime symptoms revealed 2 distinct

clinical profiles among CFS patients: (a) those with high

seasonality, for whom depressed mood clustered with atypical

neurovegetative symptoms of hypersomnia and hyperphagia, as is

seen in SAD; and (b) those with low seasonality, who showed a

primary clustering of classic CFS symptoms (fatigue, aches,

cognitive disturbance), with depressed mood most closely

associated with irritability, insomnia, and anxiety. It

appears that a subgroup of patients with CFS shows seasonal

variation in symptoms resembling those of SAD, with winter

exacerbation. Light therapy may provide patients with CFS an

effective treatment alternative or adjunct to antidepressant


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