[Upper airway obstruction in thyroid diseases]

Respiratory symptoms (stridor) in thyroid diseases are rather common, but often overlooked, especially in older people in whom they may be misinterpreted as asthma or chronic bronchitis.

To assess the value of lung function tests for differential diagnosis we used these tests in 33 patients with upper airway obstruction caused by an enlargement of the thyroid gland. The clinical examination consisted of an evaluation of the respiration, examination of the movement of the vocal chords, thyroid parameters, Tc scintigraphy, ultrasound examination, and X-ray examination of the thorax and trachea up to the level of the glottis, supplemented by a CT scan if needed. Lung function tests were carried out in all patients before and after the operation as conventional spirometry with registration of the flow-volume curve and application of peak expiratory flow (PEF), maximal expiratory and inspiratory flow at 50% of the vital capacity (MEF 50 and MIF 50) and MEF 50/MIF 50.

The surgical treatment consisted in hemithyroidectomy in 10 patients and total thyroidectomy in 23 patients. In all cases, considerable clinical improvement in respiration was achieved and the X-ray examination showed a normalisation of the lumen of the trachea. In 24 of 33 patients (73%), the flow-volume curve showed preoperatively a configuration compatible with a variable upper airway obstruction (i.e. MIF 50 < MEF 50). An increase postoperatively was found in the PEF of 21 patients (64%) and MEF 50/MIF 50 < 1 in 19 patients (58%).

It is important to distinguish between respiratory symptoms (stridor) caused by obstruction of the upper air way and dyspnoea in cardiopulmonary diseases. Lung function tests with registration of the flow-volume curve and measurement of MEF, MIF, and PEF are a useful supplement, as values indicating upper airway obstruction will be present in about 60% of the cases. Lung function tests pre- and postoperatively will serve as a good control on the effect of the operation on the thyroid gland.