Systemic calcinosis in a Quarter Horse gelding homozygous for a myosin heavy chain 1 mutation.
Authors: Sponseller Beatrice T, Wong David M, Ruby Rebecca, Ware Wendy A, Wilson Scott, Haynes Joseph S
Journal: Journal of veterinary internal medicine
Summary
# Editorial Summary: Systemic Calcinosis in a Quarter Horse with MYH1 Mutation A 9-year-old Quarter Horse gelding homozygous for a myosin heavy chain 1 (MYH1) mutation presented with lethargy, severe muscle wasting, polyuria/polydipsia, and clinical signs initially suggestive of immune-mediated myositis, prompting investigation into an underlying systemic mineralisation disorder. Laboratory and diagnostic findings revealed hallmark abnormalities including elevated muscle enzymes, hyperphosphatemia, an increased calcium-phosphorus product (>70 mg²/dL²), hypoproteinaemia, and inflammatory changes; histopathological examination of skeletal muscle, lung, and kidney biopsies confirmed systemic calcinosis—the pathological deposition of calcium phosphate in soft tissues. Treatment combined symptomatic supportive care with IV sodium thiosulfate (to chelate and reduce calcium-phosphate precipitation) and oral aluminium hydroxide (to limit intestinal phosphorus absorption), successfully reversing the condition and achieving a favourable long-term outcome. This case represents the first antemortem diagnosis and successful treatment of equine systemic calcinosis reported in the veterinary literature, and the association with homozygous MYH1 mutation suggests a genetic predisposition that practitioners should consider when investigating cases of progressive muscle wasting accompanied by secondary electrolyte and mineralisation disturbances. The successful use of medical management to address the underlying phosphorus dysregulation and ectopic mineralisation provides a template for treatment in future cases and highlights the importance of thorough diagnostic workup when immune-mediated myositis is suspected.
Read the full abstract on PubMed
Practical Takeaways
- •Systemic calcinosis should be considered in horses presenting with severe muscle wasting, fever, and signs of immune-mediated myositis; antemortem diagnosis is possible through muscle biopsy
- •Sodium thiosulfate IV combined with aluminum hydroxide PO may offer effective treatment options for reversing soft tissue calcification in affected horses
- •This case demonstrates that systemic calcinosis is not necessarily a fatal condition if diagnosed early and treated appropriately
Key Findings
- •First antemortem diagnosis of systemic calcinosis in a horse with successful treatment and favorable long-term outcome
- •Clinical presentation included lethargy, fever, severe epaxial and gluteal muscle wasting, polyuria/polydipsia, and inflammatory leukogram
- •Combination therapy with IV sodium thiosulfate and oral aluminum hydroxide successfully reversed calcium-phosphate precipitation in soft tissue
- •Histopathologic confirmation of systemic calcinosis was obtained from skeletal muscle, lung, and kidney biopsy specimens