Prevalence and predictors of low bone mineral density in Myasthenia gravis

Myasthenia gravis (MG) is an autoimmune disease affecting the postsynaptic neuromuscular junction. Treatment often includes corticosteroids, which may reduce bone mass.

To evaluate the prevalence and predictors of low bone mineral density (BMD) in MG patients.

A cross-sectional study included patients over 18 years with MG followed at the Neuromuscular Diseases Service, Hospital de Clínicas, Universidade Federal do Paraná (2018-2022). Data were obtained through clinical evaluation, medical records, MG Composite Scale, and Quantitative MG Test. Lumbar spine and proximal femur BMD were assessed using a GE Lunar densitometer, with T or Z-scores according to age/menopausal status. Logistic regression identified factors independently associated with BMD alterations.

In total, 92 patients (64.1% female, mean age: 51.3 years) were included, of whom 79.3% had early-onset MG. Past or present corticosteroid use were reported in 94.5 and 45.6%, respectively. Only 27.6% practiced regular physical activity, though most had adequate calcium intake. There were six (7.8%) patients with fragility fractures, and ⅕ were at high fracture risk according to the FRAX results. We found that BMD alterations occurred in 43.5% of patients. No significant association was found with corticosteroid use or MG severity. Age was independently associated with BMD (OR = 1.06, 95% CI: 1.03-1.09, p = 0.0005). A cutoff age ≥ 49 years yielded 82.5% sensitivity, 63.5% specificity, and an area under the ROC curve of 0.72 (95% CI: 0.61-0.83).

Reduced BMD is frequent in MG, highlighting the importance of screening and prevention of low bone mass, osteoporosis, and fragility fractures, particularly in patients over 49 years, regardless of corticosteroid use or MG severity.