Abstract Mitochondrial myopathies can manifest with dyspnea, exercise intolerance, and sleep disordered breathing. This rare condition, with a variable presentation is often misdiagnosed. Here, we present a case of undiagnosed mitochondrial myopathy masquerading as uncontrolled asthma. A 54-year-old female with a history of Hashimoto’s thyroiditis and asthma was referred to our asthma clinic for uncontrolled asthma management. She was well-controlled from her diagnosis at age 23 until 2. 5 years ago when she developed dyspnea, limiting her daily activities. Notably, she was not wheezing, and rescue albuterol was not helping. Her asthma control test score was 8. She did not respond to triple therapy and Mepolizumab. Spirometry was concerning for restriction which was confirmed on lung volumes. However, high-resolution computed tomography of the chest was normal. Cardiopulmonary exercise testing suggested a neuromuscular defect. Mean inspiratory pressure, mean expiratory pressure, and maximum voluntary ventilation were severely reduced at 26%, 12% and 38% of predicted respectively. The patient was referred to neurology for evaluation. She reported dysphonia, dysphagia, occasional blurring of vision particularly in the evening, and mild eyelid drooping. On physical examination she had proximal lower limb weakness bilaterally. Work-up for neuromuscular junction transmission disorders and neuromyopathies was negative except for elevated lactic acid and serum pyruvate at 2. 8 mMol/L and 1. 6 md/dl respectively. A nerve conduction study and electromyography were negative, however single-fiber electromyography was positive. She was trialed on pyridostigmine and prednisone for presumed seronegative myasthenia gravis; without improvement in symptoms. A muscle biopsy was unrevealing. Concern for mitochondrial myopathy was raised given persistent symptoms, lack of response to therapy and unrevealing work-up except for elevated serum lactate and pyruvate. The patient was referred to genetics for further testing. Mitochondrial DNA analysis revealed a deletion at m. 539₁4393 and m. 482₁4142 with an unclear level of heteroplasmy. A diagnosis of mitochondrial myopathy was made, and the patient was started on Creatine, Ubiquinone and Bilevel positive end-expiratory pressure at night with improvement in symptoms. In patients with asthma who have persistent dyspnea, despite escalation in treatment, with accompanying neuromuscular symptoms, it is imperative to broaden the work up. Our case is a comprehensive demonstration of a stepwise approach to the work up of unexplained dyspnea in a patient with asthma. Mitochondrial myopathies are a rare cause of dyspnea that requires a multidisciplinary approach to diagnosis and treatment. Dedicated research is needed to determine best practices and establish standardised management guidelines. This abstract is funded by: None
Safdar et al. (Fri,) studied this question.