The relationship between subclinical hypothyroidism and depression is still controversial. Our objective was to compare the prevalence of depressive symptoms and major depressive disorder in a population of patients affected by subclinical hypothyroidism and a control group without thyroid disease. The authors enrolled 123 consecutive outpatients affected by subclinical hypothyroidism undergoing follow-up at the endocrinology department of San Paolo Hospital in Milan and 123 controls without thyroid disease under the charge of general physicians.
All patients and controls underwent an evaluation by means of a psychiatric interview; Hamilton Rating Scale for Depression (HAM-D); Montgomery-Asberg Depression Rating Scale (MADRS); and serum thyroid stimulating hormone, free T4, and free T3 levels. Patients were also screened for thyroid peroxidase antibodies and thyroglobulin antibodies. Patients affected by subclinical hypothyroidism had a prevalence of depressive symptoms of 63.4% at HAM-D and 64.2% at MADRS; 22 patients (17.9%) had a diagnosis of depressive episode (Diagnostic and Statistical Manual of Mental Disorders, Fourth Edition, Text Revision criteria). The control group had a prevalence of depressive symptoms of 27.6% at HAM-D and 29.3% at MADRS, and only seven controls had a diagnosis of depressive episode. The prevalence of depressive symptoms between these two groups was statistically different. This study underlines a strong association between subclinical hypothyroidism and depressive symptoms, which could have some important diagnostic and therapeutic implications in the clinical practice.