P351 Rhabdomyolysis and muscle biopsy outcomes: a single center retrospective cohort.

Rhabdomyolysis is defined as a rapid breakdown of muscle cells, leading to the release of its proteins and enzymes causing elevation of serum creatine kinase and myoglobinuria. The muscle biopsy is an important method of assessment of these patients, as it can point to the underlying cause of the process and aid in the investigation. A retrospective study was conducted at the Institute of Myology of the Pitié-Salpêtrière Hospital, between October 1, 1996 and October 1, 2022. The study included patients that underwent muscle biopsy and with clinical presentation compatible as Rhabdomyolysis. In total, 75 patients matched the criteria. The medical records were reviewed to collected demographic data, time from last episode of rhabdomyolysis to biopsy, CPK levels and muscle biopsy data. In the population studied, we have found that 84% (63) of the patients were male. The median age was 28.16 years. The median time between the presentation and biopsy was 11.15 months and the time was unknown in 18.6% (14). Muscle biopsy was normal in 26% (20). The most frequent alteration was increased lipid content in 45,3% (34), followed by nuclei internalization, present in 44% (33). Immunohistochemistry was performed in 54,6% (41) patients. Inflammatory markers were found in 9,7% (4) and absent Dysferline in 2,4% (1). Electron Microscopy was realized in 5.3% (4) patients and there was a moderate accumulation of lipids in two samples, and accumulation of glycogen in one patient. Genetic testing was performed in 22 cases, and it was diagnostic in 68.1% (15). A diagnosis of inflammatory myopathy was done in 6.6% (5). The most frequent genetic diagnostics were RIR1 variant. The muscle biopsy with histoenzymology and immunohistochemistry is an important tool for the analysis and diagnosis of patients presenting with rhabdomyolyses. Mutations in the gene RYR1 were the most common cause of rhabdomyolysis and should be systematically searched. [ABSTRACT FROM AUTHOR]