Researchers presented the case of a woman who was initially treated with polymyositis before being correctly diagnosed as having late-onset Pompe disease (LOPD), which led to a change in therapeutic strategy, as published in the European Journal of Rheumatology.

One of the main symptoms of Pompe disease is gradual muscle weakness, followed by organ failure and death. However, the phenotype of the disease is heterogeneous, meaning that a small percentage of individuals can live close to normal lives.

A challenge in diagnosing Pompe disease is that the list of differential diagnoses is incredibly long, and physicians often misdiagnose Pompe disease as idiopathic inflammatory myosin, especially since they share key clinical and laboratory features.

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The case presented by the authors of the study details a 30-year-old woman who wanted a second opinion regarding her refractory polymyositis. This diagnosis was made 2 years ago, and despite her physicians’ best efforts, her symptoms did not improve.

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A further history-taking revealed that she began to experience dyspnea on exertion over the last 2 months. Physical examination revealed that the patient had decreased muscle strength on her proximal lower extremities and demonstrated a positive Gowers sign. 

More tests were conducted. The patient’s magnetic resonance imaging found fatty atrophic changes and muscle edema in the bilateral thigh muscles. She consented to undergo targeted genetic sequencing, which demonstrated that she was heterozygous for 2 variants in the GAA gene, which led to her new diagnosis of LOPD. She was started on enzyme replacement therapy and showed significant clinical improvements at 15 months of follow-up.

“Our patient was initially diagnosed as polymyositis and had been treated with several [immunosuppressive] therapies without clinical or laboratory improvement,” the authors said. “Therefore, it is important to consider metabolic myopathies in patients who are negative for connective tissue disease (CTD) findings and resistant to [immunosuppressive] therapies.”


Inel TY, Avsar AK, Kisa PT, et al. A challenging etiology of myopathy: the late-onset Pompe disease. Eur J Rheumatol. Published online April 5, 2022. doi:10.5152/eurjrheum.2022.21156