C42-52 Severe Restrictive Lung Disease With Normal Chest Imaging: A Case of Statin Induced Myopathy

Restrictive lung diseases are characterized by a reduction in total lung capacity and/or lung expansion. They make up almost 20% of the pulmonary syndromes and can be attributed to intrinsic pulmonary pathologies or extrinsic abnormalities, including pleural, skeletal, muscular or neuromuscular abnormalities. A 54 year old gentleman with a 40 pack year smoking history was referred to the pulmonology clinic with dyspnea on exertion, orthopnea and a cough. He had an extensive cardiac history with previous PCI and CABG, and severe hyperlipidemia and hypertriglyceridemia (>50mmol/L) with recurrent pancreatitis, managed with statin and fibrate therapy. Other medical history included Hypertension, Type 2 Diabetes and elevated BMI (34kg/m2). He worked as a cleaner, with no other occupational exposures or family history. Focused questioning revealed occasional hand weakness and paresthesia, on a background of carpal tunnel syndrome. Physical examination was unremarkable with normal resting oxygen saturations. Spirometry showed a suspected restrictive defect (FEV1 1.05L (32%) and FVC 1.24L (30%)). The patient was unable to perform lung volume testing. Spirometry in the supine position showed a reduction of 5% and 6% in FEV1 and FVC compared to those in the upright position (Image 1). Maximal Inspiratory Pressure (MIP) was normal, with significant reduction in Maximal Expiratory Pressure (MEP) at 47.94cmH2O (predicted lower limit of normal 80.70cmH2O). Cross sectional imaging was normal with no evidence of interstitial lung disease. Bloods including autoimmune panel and myasthenia gravis antibodies were normal. Creatinine Kinase (CK) was markedly elevated at 1178 U/L. A statin induced myopathy was suspected; the statin was stopped and the patient was referred to a specialist hyperlipidemia clinic to consider PCSK9 inhibitors. Bloods confirmed a genetic propensity to statin induced myopathy. Some improvement in dyspnea was seen after stopping the statin, with improvement in spirometry (FEV1 1.29L, FVC 1.68L); however, the CK level remains markedly raised (1899 U/L). A muscle biopsy, Electromyography and Nerve Conduction Studies are being pursued for a formal diagnosis. Spirometry that worsens in the supine position raises suspicion for diaphragmatic weakness or neuromuscular conditions. Multidisciplinary review of this complex patient was required to assess the risks and benefits of stopping statin therapy due to the significant co-morbidities. As this patient had ongoing dyspnea and worsening spirometry, with a risk of acute respiratory failure secondary to myopathy, stopping any contributing medication was crucial. Although symptoms and spirometry have improved since stopping the statin, the natural history of this condition is unclear.