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.