Pulmonary Physiology |

Rare Neuromuscular Disease Identified by Cardiopulmonary Exercise Testing FREE TO VIEW

Surafel Gezahegne, MD; Zachary Morris, MD
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Henry Ford Hospital, Detroit, MI

Chest. 2015;148(4_MeetingAbstracts):888A. doi:10.1378/chest.2281057
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SESSION TITLE: Pulmonary Physiology Case Report Posters

SESSION TYPE: Affiliate Case Report Poster

PRESENTED ON: Tuesday, October 27, 2015 at 01:30 PM - 02:30 PM

INTRODUCTION: Cardiopulmonary exercise testing can play an important role in identifying the presence of disease states in subjects reporting exercise limitations but otherwise appearing healthy. We describe the role of cardiopulmonary exercise testing in the identification of a rare occurrence of 2 known disease-associated mutations of the CLCN1 gene associated with myotonia congenita.

CASE PRESENTATION: A 33 year-old Caucasian male was evaluated in the pulmonary clinic for perceived excessive shortness of breath and generalized weakness during strenuous exercise for the past 2-3 years. He was a healthy appearing muscular male with no significant physical findings. A cardiology stress testing was normal with the exception of a first degree heart block on ECG. An extensive work up done for muscular and metabolic disorders including muscle biopsy, analysis of mitochondrial enzymes, and gene testing, was negative. Spirometry showed mild obstruction with normal DLCO and he reported some improvement with bronchodilators. A stage I cardiopulmonary exercise initially showed he achieved an oxygen consumption of 125% of predicted, and though anaerobic threshold was 45% of predicted maximum, it was felt to be lower than expected for an individual involved in intense daily exercise. Over the next couple of years, he felt worsening exercise tolerance. A repeat cardiopulmonary exercise showed a decline in his maximum oxygen consumption to 109% of predicted (15% reduction), with a reduced anaerobic threshold now at 37% of predicted (20% decline). There was no evidence of a pulmonary limitation. With a negative extensive cardiac evaluation, and absence of anemia, these finding were felt to be consistent with a neuromuscular etiology. Further genetic testing showed 2 distinctive recessive mutations in the CLCN1 gene, in combination causing a homozygous presentation, consistent with myotonia congenita.

DISCUSSION: Sequential cardiopulmonary exercise tests enabled clinicians to recognize the presence of a progressive neuromuscular disorder that otherwise may have gone undiagnosed. The findings prompted further testing which uncovered a rare genetic defect.

CONCLUSIONS: Cardiopulmonary exercise testing is a non-invasive test that can have an important role in the diagnostic evaluation and management of individuals with neuromuscular disorder.

Reference #1: Lossin, C., George, A.L. Myotonia congenita. Adv Genet. 2008;63:25-55.

DISCLOSURE: The following authors have nothing to disclose: Surafel Gezahegne, Zachary Morris

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