Pulmonary consequences of hypothyroidism

Although hypothyroidism has an insidious onset and relatively asymptomatic, exertional dyspnea and fatigue can be the presenting complaints.

The aim is to assess functional lung impairment in hypothyroid patients both at rest and during exercise.

A case-control study was carried out on 42 patients with newly diagnosed hypothyroidism and 12 control subjects. Hypothyroidism was diagnosed based on high value of thyroid stimulating hormone (TSH) ≥6 μIU/ml, and low value of free thyroxin (FT4) ≤0.8 ng/dl, both groups had chest X-ray, spirometry, diffusing capacity of the lungs for carbon monoxide (DLCO), arterial blood gases (ABGs) and symptom-limited exercise testing using treadmill.

Both groups were comparable as regard age, sex, and body mass index. Although ABG and spirometry were within normal in both groups, forced vital capacity %, and forced expiratory flow (FEF_25-75) % were significantly reduced in the hypothyroid group (P = 0.014, 0.000, respectively), DLCO significantly reduced in hypothyroidism (P = 0.005). As regard exercise testing parameters, maximum oxygen consumption %, minute ventilation, tidal volume, and oxygen pulse were significantly reduced in hypothyroidism (0.005, 0.000, 0.000, and 0.02 respectively). TSH significantly negatively correlated with forced expiratory volume in 1 s %, FEF_25-75%, and DLCO while they significantly positively correlated with FT4.

Even with the presence of normal chest X-ray, arterial blood gases, and spirometry in patients with hypothyroidism DLCO and exercise testing parameters can be significantly reduced.