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letter
. 2007;9(6):467–468. doi: 10.4088/pcc.v09n0611d

Hypothyroidism in Patients With Asthma and Major Depressive Disorder

Rebecca J Oppedal 1, David A Khan 2, E Sherwood Brown 3
PMCID: PMC2139917  PMID: 18185831

Sir: Approximately 8% of depressed patients have at least subclinical hypothyroidism,1 compared to only 5% of the general population.2 An epidemiologic study found that hypothyroidism may also be associated with asthma,3 although this association is less well established than the association with depression. Depression is extremely common in asthma patients.4 Thus, depressed asthma patients may be a population at especially high risk for hypothyroidism. To our knowledge, no data are available examining thyroid abnormalities in depressed asthma patients. This study evaluated the relationship between depression, thyroid disease, and asthma severity in asthma patients with current depression.

Method

This investigation examined 90 participants with asthma and major depressive disorder (MDD) from a clinical trial conducted between March 2002 and December 2003 on the treatment of depression in asthma patients.5 The study received institutional review board (IRB) approval, and all participants provided IRB-approved informed consent. Adult outpatients who had asthma and current MDD with a 17-item Hamilton Rating Scale for Depression (HAM-D)6 score of at least 17 were included in this study. No participants were taking medication for depression at the time of assessment.

Major depressive disorder was diagnosed using the Mini-International Neuropsychiatric Interview.7 Thyroid disease was diagnosed using both clinical history (e.g., physician diagnosis of hypothyroidism and patient taking thyroid supplementation) and laboratory analysis of thyroid-stimulating hormone (TSH) levels; TSH levels were obtained at study enrollment. Asthma symptoms were assessed using the Asthma Control Questionnaire (ACQ).8 Two-tailed t tests and Pearson correlations were used to determine significance.

Results

This investigation examined the history of thyroid disease in 90 participants. The participants were 78.7% female with a mean ± SD age of 40.1 ±10.2 years; 6.7% were white, 58.2% were Hispanic, and 33.3% were African American; and the group had a mean ± SD forced expiratory volume in 1 second percentage (FEV1%) predicted of 73.4 ± 20.9%.

Four (4.4%) of the 90 patients had a clinical history of hypo-thyroidism, and 1 (1.1%) had a history of hyperthyroidism, making the total prevalence rate of a clinical history of thyroid disease 5.5%. Of these 90 participants, 75 were included in the analysis of TSH values. Eleven participants were excluded because baseline TSH scores were not available, and 4 were excluded because they were taking thyroid supplementation that would artificially suppress TSH levels. The 4 participants excluded based on the use of thyroid supplementation were the 4 participants with a history of hypothyroidism discussed above.

Mean ± SD TSH level was 1.9 ± 1.2 mIU/L (range, 0.18–6.10 mIU/L). Of the 75 patients analyzed, 7 patients (9.3%) had TSH levels outside the normal range (0.5–5.5 mIU/L), including 2 patients (2.7%) with high values and 5 patients (6.7%) with low values. A total of 2 (2.7%) of 75 patients showed hypothy-roidism based on TSH levels. Therefore, combining information obtained from the 4 participants with a clinical history of hypo-thyroidism and the 2 participants with elevated TSH levels, the lifetime prevalence rate of hypothyroidism in our population was 6 of 90 patients, or 6.7% (95% CI = 3.1 to 13.8).

No significant correlation was found between TSH levels and HAM-D scores (r = 0.03, p = .82). Asthma Control Questionnaire scores, however, showed a significant negative correlation with TSH values (r = −0.24, p = .04).

Hypothyroidism, based on combined clinical history data and elevated TSH values, was found in 6.7% of patients with MDD and asthma. This finding is similar to that reported in general samples of MDD patients. Therefore, asthma does not appear to increase the risk of hypothyroidism in MDD.

Of note is that 5 participants had low TSH values without taking thyroid supplementation. The clinical significance of this finding is difficult to interpret without triiodothyronine (T3) and free thyroxine (FT4) data, but possible explanations include subclinical hyperthyroidism,9 central hypothyroidism, euthyroid sick syndrome,10 and recent use of oral corticosteroids.11 Thus, the prevalence of either hyperthyroidism or hypothyroidism may actually be slightly higher than reported.

Thyroid-stimulating hormone levels were not related to depression severity. However, a significant negative correlation was found between ACQ values and TSH levels, suggesting a potential association between asthma control and TSH levels.

Acknowledgments

Funded by National Institutes of Health grant MH63133 (Dr. Brown). Dr. Brown has received grant/research support from AstraZeneca, Forest, GlaxoSmithKline, UCB Pharma, McNeil, National Institute on Alcohol Abuse and Alcoholism, and Stanley Medical Research Institute and serves on the advisory board of Bristol-Myers Squibb. Ms. Oppedal and Dr. Khan report no financial or other relationships relevant to the subject of this letter.

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Articles from Primary Care Companion to The Journal of Clinical Psychiatry are provided here courtesy of Physicians Postgraduate Press, Inc.

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