INTRODUCTION: Exogenous steroid therapy may cause respiratory muscle weakness. Although prolonged endogenous excess of steroids in Cushing's Syndrome (CS) may causes severe weakness in the limb muscles, the respiratory muscle strength and pulmonary functions are usually spared (1). We report a case of reduced lung volumes associated with ectopic adrenocorticotrpic hormone (ACTH) secretion due to thymic carcinoid of the lung.
CASE PRESENTATION: A 27-year-old nonsmoker male presented with low back pain, weight-gain, and proximal muscle weakness of several months duration. Further work up showed a high urinary cortisol and non-suppressible elevation of ACTH in the serum (123 pg/ml (7-69)). The Insulin like growth factor IgF1 was significantly reduced 62 ng/mL (117-329). A CT scan of the chest and abdomen was normal. Preoperative pulmonary function test revealed the following: FVC 2.53 L (48 %), TLC 4.31 L (65%), VC 2.98 L (56%), DLCO 57% and DL/VA 101% of predicted. These findings were consistent with restrictive lung disease. On testing respiratory muscle forces, maximal inspiratory pressure (MIP) was 130 cmH2O (101% of predicted) and maximal expiratory pressure (MEP) was 100 cmH2O (42% of predicted). This was suggestive of expiratory muscle weakness. An octreoscan identified two areas of abnormality in the right chest consistent with somatastatin receptor positive lesions, which were resected using the nuclear medicine detection device. The histopathology showed an ACTH producing thymic carcinoid. On follow up six months after surgery the patient recovered and is asymptomatic. Despite of no change in BMI (21.7 and 21 Kg/m2, pre and 6 months post-op, respectively), there were significant increases in the lung volumes FVC 4.1 L (70 %), and TLC 6.8 L (93%). His DL/VA 6 months postoperatively was 81 % of predicted. A repeat MIP and MEP were 97 cm H2O (76%) and 85 cm H2O (36%), respectively. The ACTH level decreased from 143 to 40 pg/ml, and the IgF1 had increased from 62 to 210 ng/mL (117-329) six months postoperatively.
DISCUSSIONS: Our patient presented with restrictive lung disease and weakness of the expiratory muscles. His lung volumes and IgF1 increased, while the ACTH decreased following treatment. The reduction in lung volume could be due to respiratory muscle weakness, obesity, or parenchymal lung disease. On follow up, however, in spite of lower MIP and MEP, his FVC and TLC increased. The BMI did not change significantly and the chest CT scan did not suggest any parenchymal lung disease. Previous studies have shown impaired GH secretion in patients with active CS. Patients with low GH have been shown to have reduced lung volumes. This restrictive defect was related to the decrease in lung size and not neuromuscular impairment or chest wall mechanics abnormality (2). Expiratory muscle weakness, however, has less impact on respiratory function. The paralleled GH increase after surgery with the improvement in lung volumes raises the possibility of GH effect on the later in adults.
CONCLUSION: CS is usually not associated with respiratory muscle weakness or restriction (1). We present a rare case of CS due to pulmonary carcinoid tumor, who had reduced lung volumes and expiratory muscle weakness. The reduced lung volumes are not completely explained on the basis of respiratory muscle weakness or obesity, thus raising the possibility whether this is secondary to GH deficiency. GH deficiency has been shown to influence the lung volumes in adults leading to restriction. The relationship between the GH and lung volumes needs to be further investigated.
DISCLOSURE: Abdul Ghani Sankri-Tarbichi, None.