Clearance of technetium-99m-labeled DTPA in hyperthyroidism without clinical evidence of lung disease, and relation to pulmonary function.

OBJECTIVE The mechanisms of dyspnea and exercise intolerance have not been fully elucidated. We aimed to investigate the clearance rate of technetium-99m diethyltriaminepentaaceticacid (Tc-99m DTPA) from lungs in hyperthyroid patients without clinical evidence of lung disease and to explore the interactions between their Tc-99m DTPA radioaerosol lung scintigraphy, spirometric measurements, and the levels of thyroid hormones. METHODS We studied 19 hyperthyroid patients and 16 sex- and age-matched controls. Thyroid hormone levels were assessed. Spirometric lung function tests, diffusing capacity of the lung for carbon monoxide (DLCO) and the clearance rate of Tc-99m DTPA were performed in all participants. Ratio of DLCO value to the alveolar ventilation (DLCO/VA) and the means of half-time (T1/2) of Tc-99m DTPA clearance rate, which were used to evaluate alveolar-capillary membrane permeability, were calculated. RESULTS There were no statistical differences between spirometric parameters (VC, FVC, FEV1/FVC, FEF 25-75) of the two groups (p > 0.05). Although the mean FEV1 level was significantly lower in the hyperthyroid patients than the control subjects (p < 0.01), in five patients FEV1 was only less than 80 percent of the predicted value. No significant difference in the means of DLCO, DLCO/VA or T1/2 values of Tc-99m DTPA clearance was observed between the two groups (p > 0.05). In hyperthyroid patients, there was a positive relation between DLCO/VA, DLCO/VA % and T1/2 values of Tc-99m DTPA clearance (p < 0.01, r = 0.732, p < 0.01, r = 0.742, respectively). The lung volumes and the levels of thyroid hormones did not show a significant relationship to T1/2 values of Tc-99m DTPA clearance in hyperthyroid group (p > 0.05). CONCLUSIONS We conclude that increased thyroid hormones have no effect on permeability of alveolar-capillary membrane in hyperthyroid patients.