Calcinosis Circumscripta with Iron Mineralization in an African Green Monkey (Chlorocebus aethiops sabaeus)

A 19-y-old, colony-born, female African green monkey (Chlorocebus sabaeus) presented for recurrent swelling measuring 11 × 5 × 4 cm on the right thigh, around the stifle, which started 5 y previous, resulting in lameness. The affected area had alopecia and crusting and felt lobulated on palpation. Radiographic evaluation revealed multiple foci of well-circumscribed, soft-tissue mineralization within the subcutis and underlying muscles. The monkey was euthanized due to poor quality of life. Postmortem exam demonstrated a yellow-to-red, friable, crepitant, nonencapsulated multilobulated mass, infiltrating skeletal muscles of the right thigh and containing multiple white hard spicules. Microscopic examination revealed abundant irregular-to-globoid amphophilic material (mineralization) in the subcutis and skeletal muscle. The mineralization was surrounded by extensive fibrous connective tissue (fibrosis), lymphocytes, macrophages, and multinucleated giant cells. Histochemical staining, scanning electron microscopy, and infrared spectroscopy determined the mineral material to be composed of calcium phosphate and small amounts of collocated iron. The findings were most consistent with a diagnosis of calcinosis circumscripta (sometimes referred to as tumoral calcinosis). Calcinosis circumscripta in African green monkeys has not previously been reported, although this condition has been reported in rhesus macaques, a common marmoset, and a cynomolgus macaque. The cause of iron mineralization in this case was unknown, and its occurrence within calcinosis lesions has not been previously documented.