Hypothyroidism and Depression: Are Cytokines the Link?

Primary hypothyroidism has been thought of as an inflammatory condition characterized by raised levels of cytokines such as C-reactive protein (CRP), interleukin-6 (IL-6), and tumor necrosis factor-alpha (TNF-α). Depression is also well known to occur in hypothyroidism. Depression is also characterized by elevated inflammatory cytokines. We planned to study whether cytokines play an important part in linking these two conditions.

(1) To know the prevalence of depression in overt hypothyroidism due to autoimmune thyroid disease. (2) To correlate the levels of inflammatory markers with the occurrence of depression. (3) To study the effect of levothyroxine on inflammatory markers and depression.

In this longitudinal, case-controlled study, 33 patients with autoimmune hypothyroidism (thyroid-stimulating hormone >10 uIU/ml) were included with 33 age-, sex-, and body max index-matched healthy controls. Individuals were tested for Serum TNF-α, IL-6, high-sensitivity-CRP (hs-CRP). They were assessed for depression using Montgomery Asberg Depression Rating Scale (MADRS) and World Health Organization Quality of Life (QOL) Scale. Patients received L Thyroxine titrated to achieve euthyroidism and were reassessed for inflammatory markers and cognitive dysfunction.

Nineteen patients (57%) had mild to moderate depression (MADRS >11). After 6 months of treatment, eight patients (42%) had remission of depression with significant improvement in QOL scores (P < 0.05). TNF-α, IL-6, and hs-CRP were significantly elevated in patients compared with controls and reduced with therapy but did not reach baseline as controls. The change in inflammatory markers correlated with improvement in QOL scores in social and environmental domains (P < 0.01).

Primary autoimmune hypothyroidism is an inflammatory state characterized by elevated cytokines which decline with LT4 therapy. It is associated with depression and poor quality of life. Treatment of hypothyroidism results in alleviation of depression in the majority of patients. Similarly, patients with mild to moderate depression should be tested for hypothyroidism as simple treatment may ameliorate their depression and improves MADRS score and QOL.