Introduction
Systemic mastocytosis (SM) is a clonal disorder of mast cells and is a rare cause of osteoporosis. The prevalence of osteoporosis is about 20-28% in patients with indolent systemic mastocytosis (ISM) (1)(2) with the spine being the predominating site involved (3). We report two cases of osteoporosis secondary to ISM presenting with vertebral fractures.
Cases
A 47-year-old Pakeha male farmer presented following low-trauma multi-level vertebral fractures. DEXA bone mineral density (BMD) scan confirmed osteopenia of L1-L4 spine (T-score -2.3 SD and Z-score of -2.6 SD). His past medical history included asthma, ex-cigarette smoker, current cannabis use, moderate alcohol intake and previous carpal tunnel release. He had been diagnosed with cutaneous mastocytosis 4 years prior however, was not on treatment for this. Medications included asthma inhalers and proton-pump inhibitor for reflux. Extensive investigation did not reveal an underlying endocrine cause of fragility fracture. The diagnosis of indolent systemic mastocytosis was confirmed with elevated tryptase 26.1 ug/L (RI 0-10), bone marrow aspirate confirmed the presence of an aberrant population of mast cells and cKIT D816V mutation detected on molecular studies. He was started on vitamin D supplementation and bisphosphonates with a plan to repeat BMD after 2 years. He takes antihistamine medication for symptom relief and remains on surveillance for progression of systemic mastocytosis.
A 72-year-old New Zealand European female presented following low trauma L2 vertebral compression fracture and BMD T score -2.9 SD of the spine. Menopause was at age 50, followed by hormone replacement therapy (HRT) until age 68. She kept active and was a lifelong non-smoker. She had a long-standing rash on her thigh, a biopsy done 10 years prior suggested cutaneous mastocytosis. Other past medical history includes a platelet function disorder, previous cholecystectomy, hysterectomy and right total knee joint replacement. Investigations excluded underlying endocrine causes of osteoporosis but found she had an elevated tryptase (28.4ug/L {RI 0-10}) and positive cKIT D816V mutation. She is currently awaiting a bone marrow biopsy with the working diagnosis of indolent systemic mastocytosis. Current management is with Vitamin D replacement and bisphosphonates.
Conclusion
These cases highlight ISM as a rare but important cause of secondary osteoporosis. The diagnosis should be considered when common secondary causes of osteoporosis are excluded or in patients with features of cutaneous mastocytosis and elevated tryptase.
take home points
- Systemic mastocytosis is a rare but recognised cause of osteoporosis, often involving the vertebra.
- Osteoporotic fractures may be the first clinical presentation of the condition, sometimes in addition to cutaneous mastocytosis rash.
- When there is clinical suspicion, initial investigations include tryptase levels and cKIT D816V mutation molecular studies, in addition to Haematology input.
- Osteoporosis treatment involves treating underlying haemtological condition if indicated, in addition to usual osteoporosis treatment, in our cases, bisphosphonates were prescribed.
References