Prevalence of diaphragmatic muscle weakness and dyspnoea in Graves' disease and their reversibility with carbimazole therapy.

Objectives: Dyspnoea is a common complaint among patients with thyrotoxicosis. However, its causative mechanisms have not been identified. We assessed the role of thoracic diaphragmatic muscle weakness in dyspnoea among patients with active Graves' disease.

Methods: Twenty-seven patients (19 female, 8 male) with active Graves' disease were assessed for the clinical severity of dyspnoea, functional (pressure generating capacity) and anatomical aspects (thickness and excursion) of the diaphragm at presentation. The severity of dyspnoea was assessed using a visual analogue scale (VAS) and the 6 min walk test. Lung function tests, diaphragmatic strength (sniff oesophageal pressure, SniffP(oeso)), maximum inspiratory and expiratory pressures, diaphragmatic thickness and movements on real time ultrasonography were evaluated during normal and deep respiration. Twenty of the 27 patients were reassessed after achieving euthyroidism with carbimazole therapy at a mean interval of 5+/-2 months.

Results: Reevaluation after carbimazole therapy revealed a significant reduction in dyspnoea on the VAS (59+/-26 to 23+/-13%). Patients covered a similar distance during the 6 min walk before and after euthyroidism. Significant improvement was observed in the vital capacity (2.57+/-0.62 to 2.94+/-0.60 l), forced expiratory volume in the first second (2.21+/-0.49 to 2.45+/-0.47 l), total lung capacity (3.57+/-1.19 to 4.1+/-1.12 l), diaphragmatic movement during deep respiration (5.5+/-1.0 to 6.6+/-1.1 cm) and SniffP(oeso) (68.7+/-23 to 93.1+/-25.2 cmH(2)O). There was no significant change in the distance walked in 6 min, tidal volume, lung diffusion capacity and diaphragmatic thickness. There was no significant correlation between the net change in dyspnoea score and net change in lung function tests, diaphragmatic movement and SniffP(oeso).

Conclusions: Significant functional weakness of diaphragm muscle is present in patients with active Graves' disease. This weakness is more marked during a maximal respiratory manoeuvre, indicating a diminished diaphragmatic reserve which could be the cause of dyspnoea observed on exertion among patients with thyrotoxicosis.