This report highlights the rare histopathological characteristics observed in a patient with STIM1-associated tubular aggregate myopathy type 1. Understanding these features may provide insights into the clinical presentation and underlying pathophysiology of this condition.

A 17-year-old female was referred for evaluation of progressive proximal weakness. Her development was normal until age two, when she experienced meningitis, resulting in a brief regression in walking. Despite this, she continued to develop cognitively and physically, with mild symptoms of reduced activity and fatigue starting around age ten. Over the past three years, she exhibited clear weakness, particularly in her lower extremities, requiring support to rise from a seated position and experiencing noticeable muscle loss. Importantly, she reported no sensory symptoms or cognitive impairment and was performing well academically. The patient also experienced intermittent nosebleeds, occurring weekly to monthly. Family history was unremarkable for similar conditions. Examination revealed intact higher mental functions and cranial nerves. Musculoskeletal assessment noted left shoulder winging, bilateral little finger contraction, scoliosis, and lordosis, with symmetric muscle power (4/5 in proximal upper limbs and 4-/5 in proximal lower limbs). Laboratory tests indicated significant hyper-CKemia (4454 U/L) and borderline liver enzyme elevation. Electromyography demonstrated myopathic changes without inflammatory signs. A left vastus lateralis biopsy revealed an active myopathic/dystrophic picture with inflammation, tubular aggregates, and type 2 atrophy. Whole exome sequencing identified a heterozygous variant of uncertain significance in the STIM1 gene (c.241G>T; p.Gly81Cys), consistent with tubular aggregate myopathy.

This case illustrates the unique combination of dystrophic features and inflammation in a patient with STIM1-associated tubular aggregate myopathy. The presence of tubular aggregates, while seen in various conditions, in conjunction with a STIM1 mutation, reinforces the need for careful classification and further investigation of this rare myopathy.