To the Editor:
Dr Dutt and colleagues aptly call attention to the high probability of undiagnosed subclinical hypothyroidism (HT) being present among patients included in our article recently published in CHEST (September 2015)1 Because thyroid function tests (TFTs) were not performed for most patients with idiopathic pulmonary fibrosis (IPF), those who had subclinical HT, which is more prevalent than overt HT,2 may have been missed. On review of patients with IPF without known HT, for whom TFTs were available (n = 65), elevated thyroid-stimulating hormone (TSH) was observed in six. Two were subsequently diagnosed with overt HT, one with non-thyroidal illness syndrome, and three with subclinical HT, which supports the observation of these authors.
Whether patients with undiagnosed subclinical HT were denied treatment with thyroid replacement therapy remains debatable, as TSH variability increases with age and treatment of a marginally elevated TSH level is of unproven benefit.3 The prevalence and clinical consequences of subclinical HT in patients with IPF certainly deserve further investigation because of the increased mortality risk associated with overt HT in this patient population. To facilitate such research and identify those with undiagnosed overt HT, we recommend systematic collection of TFTs in all patients with suspected IPF.
These authors also noted that treatment with systemic corticosteroids, which may lead to HT through TSH suppression,4 is often of shorter duration and less cumulative dose in patients with COPD compared to those treated with historical IPF regimens. Whereas we agree with this statement in general, we adjusted only for chronic systemic corticosteroid use in our analysis. The high percentage of chronic systemic corticosteroid use among COPD control subjects in our study likely reflects a high severity of disease, as we are a major referral center for patients with advanced obstructive lung disease. Finally, if chronic systemic corticosteroid use were a major confounder in our analysis, we would expect to see more variability in the HT OR produced by our adjusted and unadjusted logistic regression models.
Footnotes
FINANCIAL/NONFINANCIAL DISCLOSURES: The authors have reported to CHEST the following: M. E. S. has received institutional grants from the National Institutes of Health (NIH); Bristol-Myers Squibb; Gilead Sciences, Inc; Intermune; and MedImmune for the conduct of clinical trials in IPF. She has received honoraria for serving on a Data Monitoring Committee for Boehringer-Ingelheim GmbH and an advisory board for Intermune. I. N. has received honoraria for advisory boards with Boehringer-Ingelheim GmbH; Intermune; and Anthera Pharmaceuticals, Inc within the last 12 months related to IPF. He has also received speaking honoraria from GlaxoSmithKline and receives consulting fees from Immuneworks. He also has study contracts with the NIH, Stromedix, Sanofi SA, and Boehringer-Ingelheim GmbH for the conduct of clinical trials in IPF. None declared (J. M. O.).
FUNDING/SUPPORT: This investigation was supported by a National Institutes of Health T32 training grant [T32-HL007605].
References
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