Severe Acquired Idiopathic Thrombocytopenia in a Female Cynomolgus Macaque (Macaca fascicularis)

A 4-y-old female cynomolgus macaque presented for veterinary evaluation prior to placement in a preclinical study showed markedly low platelet counts that continued to decrease over time. Physical examination over the next several days showed areas of pale red discoloration in forelimbs, anterior thorax, and inguinal area and multifocal pinpoint areas of erythema or scabs. An area of dark red discoloration approximately 2 cm in diameter on the dorsal surface of the tongue was discovered on day 9. The macaque was euthanized, and histopathologic evaluation showed multifocal, ulcerative or erosive, hemorrhagic, lymphohistiocytic and neutrophilic glossitis and tonsillitis. The lesions on the tongue were associated with opportunistic fungi consistent with Candida albicans. The bone marrow showed megakaryocytic hyperplasia. There was no evidence of increased consumption of platelets, sequestration of platelets, or bone marrow suppression. The monkey was serologically negative for simian retrovirus, SIV, and simian T-lymphotropic virus. In light of cases reported in humans, immune-mediated destruction of platelets due to autoantibodies secondary to Candida albicans infection was considered. However, we were unable to detect antiplatelet antibodies on the platelet surface or in serum to support this etiology; therefore idiopathic thrombocytopenia was diagnosed. To our knowledge, this case represents the second reported observation of acquired thrombocytopenia in a nonhuman primate and the first reported observation in a cynomolgus macaque.Abbreviations: SVV, simian varicella virusDrug-induced thrombocytopenia is a serious but relatively common clinical condition, because numerous drugs have been associated with development of DIT. The diagnosis of drug-induced thrombocytopenia is usually made after the exclusion of all other possible causes, such as infectious agents and artifactual decreases due to clumping of platelets in vitro (pseudothrombocytopenia), and the establishment of a temporal relationship between the administration of a drug and the development of thrombocytopenia. Consequently, scientists involved with preclinical studies in NHP need to be aware of nondrug-related cases of unexplained marked thrombocytopenia like the one we describe in this case report because they may confound a drug-related effect.