Introduction:​ Methotrexate (MTX)-related osteopathy is rare, defined by the triad of pain, osteoporosis, and “atypical fractures” when it was first described in the 1970s in children treated with high doses MTX for acute leukemia. Since then, several cases have been reported in patients treated with low-dose MTX for inflammatory diseases.

Methods:​ A systematic research of cases of MTX-related osteopathy was performed in records of Rheumatology Department of Rennes University Hospital. Data collection focused on demographic data, corticosteroid doses, MTX doses and intake method, cumulative doses, year of diagnosis, fracture location, bone densitometry value, and osteoporosis treatment if necessary. A literature review was also conducted to identify other cases in literature and try to understand the pathophysiological mechanisms of this rare entity.

Results:​ We report 5 cases identified between 2011 and 2019, which represents the largest cohort described excluding oncology cases. Fracture locations were atypical for osteoporotic fractures. All patients improved in the following months with MTX withdrawal. All patients except one were treated with antiresorptives (bisphosphonates, denosumab). Two patients, treated with bisphosphonates, had a recurrence of fracture, once again of atypical location. Twenty-five cases were collected in literature with similar clinical presentation. The cellular studies that investigated the bone toxicity of MTX mainly showed a decrease in the number of osteoblasts, osteocytes, and chondrocytes in the growth plate and an increase in the number and activity of osteoclasts. In vitro, consequences of mechanical stimulation on human trabecular bone cells in the presence of MTX showed an alteration in mechano-transduction, with membrane hyperpolarization, acting on the integrin pathway. In contrast with our report, the cases described in the literature were not consistently associated with a decrease in bone mineral density (BMD).

Conclusion:​ MTX osteopathy while rare must be known by the rheumatologist, especially when using this treatment for inflammatory conditions. The mechanisms are still poorly understood, raising the question of a possible remnant effect of MTX on osteo-forming bone cells, potentially dose-dependent.

Mini-abstract:​ Methotrexate (MTX) osteopathy, described as a clinical triad, pain, osteoporosis, and atypical stress fractures, while rare, must be known by the rheumatologist. Our cohort of 5 cases represent the largest series of the literature. Pathophysiological studies raised the question of a dose-dependent remnant effect of MTX on osteo-forming bone cells.