In addition, the authors compared systemic steroids used by patients with IPF and those used by control subjects who had COPD to exclude the possibility of corticosteroids as a cause of hypothyroidism. However, the pattern of systemic steroid use in COPD and IPF is different. In COPD, systemic steroids are usually used for short durations in the setting of an acute exacerbation whereas in IPF, when steroids are used it is for a longer duration, resulting in a higher cumulative dose. Hypothyroidism associated with steroids has been seen to be dose dependent. Thus, corticosteroid use may also be a contributing factor in the increased prevalence of hypothyroidism seen in the study.