Abstract Details

Title Concurrent Inclusion Body Myositis and Late Onset Pompe Disease: A Case Report

Topic Neuromuscular and Clinical Neurophysiology (EMG)

Presentation(s) P7 - Poster Session 7 (5:00 PM-6:00 PM)

Poster/Presentation
Number 11-014

Objective NA

Background

Late-onset Pompe disease (LOPD) is an autosomal recessive disorder due to pathogenic mutations in GAA leading to partial deficiency of acid alpha-glucosidase (GAA) enzyme activity, proximal muscle weakness, respiratory insufficiency, and onset after the age of 12 years. Inclusion body myositis (IBM) is typically sporadic with asymmetric, slowly progressive quadricep and finger flexor weakness with approximately 50% of patients having autoantibodies to cytosolic 5’ nucleotidase 1A (anti-cN1A). Here we present a patient with concurrent IBM and LOPD.

Design/Methods NA

Results This is a 57-year-old female with history of chronic nephritic syndrome status post kidney transplant who presented with multiple years of slowly progressive hand weakness and proximal girdle weakness. Neurologic exam revealed mild proximal muscle weakness, mild ankle dorsiflexion and toe extensor weakness, severe asymmetric hand weakness most prominent in the distal finger flexors, and significant atrophy of anterior forearm musculature. Repeat examination 6 months later revealed mild, asymmetric quadricep atrophy with preserved knee extension strength. EMG revealed a multifocal myopathy with muscle fiber irritability, scattered myotonic discharges in limb muscles, and prominent high-frequency myotonic discharges in thoracic paraspinal muscles. Creatine kinase level was normal. Initial anti-cN1A testing was normal though repeat 8 months later was mildly elevated. Genetic testing was negative for myotonic dystrophy types 1 and 2 but testing for Pompe disease revealed two pathogenic mutations in GAA confirmed in trans via parental testing. GAA enzyme activity was abnormal, consistent with LOPD. Enzyme replacement therapy was subsequently started. Given atypical presentation, muscle biopsy was performed showing an active myopathy with large vacuolar fibers, numerous ragged red fibers, and perinuclear and nuclear filamentous inclusions. These findings are consistent with both LOPD and IBM.

Conclusions This case highlights the importance of maintaining clinical suspicion for rare, overlapping diseases when clinical phenotype or laboratory findings are inconclusive especially given availability disease-specific therapies.

Authors/Disclosures
Brianna Brun (Strong Memorial Hospital) PRESENTER	Dr. Brun has received research support from National Institute of Neurological Disorders and Stroke.
Alexander Tran, Medical Student	Mr. Tran has nothing to disclose.
Lauren B. Adams, Undergraduate Student	Miss Adams has received research support from NIH SURF Grant summer 2024.
Shawn P. Jorgensen, MD	Dr. Jorgensen has nothing to disclose.

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