Background
Skeletal muscle diseases include a wide range of disorders that are often challenging to diagnose due to overlapping clinical and histological features. Electron microscopy (EM) can provide valuable ultrastructural detail when other investigations are inconclusive. This service evaluation aimed to assess the diagnostic value of EM in skeletal muscle biopsies by determining how often it contributed additional diagnostic information in routine practice.
Methods
A total of 84 reports were reviewed from the Leeds Teaching Hospital Trust database between 2018 and 2025. Cases were evaluated by two reviewers along with oversight from a consultant histopathologist. EM findings were compared with light microscopy results and categorised as either providing additional diagnostic value or not. Data were summarised descriptively in Microsoft Excel, and the diagnostic yield with 95% confidence intervals was determined using the Wilson method.
Results
EM contributed additional diagnostic value in 67 of the 84 reviewed cases (79.8%). The greatest yield was observed in mitochondrial myopathies (95.6%) and inflammatory myopathies (73.3%). In contrast, biopsies showing minimal or no structural abnormalities demonstrated a lower yield (57.1%). While EM findings rarely changed the diagnosis when light microscopy results were already conclusive, they were particularly helpful in confirming or ruling out mitochondrial pathology.
Conclusions
EM continues to provide useful diagnostic information in selected conditions while being most useful for mitochondrial and structural myopathies. It is best used as a complementary technique to light microscopy and genetic testing. This supports targeted rather than routine use.

Electron microscopy (EM) is pivotal in renal pathology, yet its diagnostic power beyond the glomerulus remains underutilised and, at times, overlooked. Although EM is routinely associated with glomerular disease, it is uniquely positioned to identify critical ultrastructural abnormalities within tubulointerstitial and vascular compartments, findings that frequently determine diagnosis, refine classification, and directly influence clinical management. This presentation challenges the glomerulocentric paradigm by highlighting the role of EM in non-glomerular renal pathology.