Iridophoroma in Leopard Geckos (Eublepharis macularius): Clinical Complications and Histopathology
Leopard geckos (Eublepharis macularius) with lemon frost morphologies are predisposed to iridophoroma, attributed to a tumor suppressor gene mutation also associated with melanoma in humans. In this case series, we describe the clinical presentation, diagnostics, complications, and pathology of iridophoroma in 4 adult leopard geckos, including 2 super lemon frost females and 2 lemon frost males. All animals presented with hyporexia, intermittent lethargy, weight loss, submandibular masses, and oral plaques. In addition, females demonstrated asymmetric coelomic distension, and one male developed altered mentation. Initial differential diagnoses included metabolic disorders, gastrointestinal infectious diseases, and neoplasia. During clinical management of these cases, ultrasonography revealed hyperechoic hepatic nodules in all animals. Fine needle aspiration (FNA) of the subcutaneous submandibular masses found clusters of mesenchymal cells with abundant cytoplasm containing fine birefringent granules. Due to continued decline and poor prognosis, animals were euthanized and submitted for necropsy. Gross examination of all 4 geckos demonstrated skin thickening by white masses throughout the body and multifocal white hepatic plaques. Two females showed yellow, enlarged ovaries, and one of the males had hard intraluminal debris in the urinary bladder. Histopathology of the skin throughout the body showed the dermis and subcutis were infiltrated by myriad pleomorphic, ovoid to fusiform, brown-pigmented neoplastic cells characterized by abundant birefringent intra- and extracellular granules. FNA, ultrasound, necropsy, and histopathology results were consistent with diagnosis of malignant iridophoroma with metastasis to multiple visceral organs including the brain and ovary. In addition, both females developed preovulatory follicular stasis (POFS)-associated oophoritis, and one of the males demonstrated urolithiasis; all of which were considered as metabolic imbalance-related pathology due to hyporexia or tumor invasion. This report illustrates the diagnostic features of FNA, ultrasound, and histopathology of malignant iridophoroma in leopard geckos. It also discusses POFS and urolithiasis as multisystemic sequelae to malignant tumors in geckos.
Presenting Leopard Gecko Appearance. (A) Dorsal and (B) ventral male lemon frost. (C) Dorsal and (D) ventral female super lemon frost. The difference in yellow to white coloration between the morphologies is of note, alongside the presence of clinical signs including (B) bilateral ventral dermal thickening and (D) coelomic mass development.
Leopard Gecko Clinical Exam. (A) Oral plaques (arrow) and unilateral submandibular mass (square) that initiated as dermal thickening. (B) Multiple clusters of fusiform cells noted on cytology after FNA of submandibular mass. There are several erythrocytes in the periphery. Granules with birefringence were confirmed by microscopic observation under polarized light (not shown).
Leopard Gecko Physical and Corresponding Ultrasonographic Exam. (A) A large mass was visualized on external exam of gecko I, prompting further diagnostics. This mass appeared heterogeneous, expansile, and cavitated on ultrasonographic exam both in longitudinal (blue) and transverse (red) views. (B) Representative images of well-demarcated, hyperechoic lesions which were visualized on hepatic ultrasonography of all 4 animals (circle).
Representative Lesions From Gross Examination of Multiple Animals. (A) White plaques in the caudal oral cavity. (B) Submandibular dermal thickening and focal coalescence of white infiltrate. (C) Axillary infiltration of the endolymphatic sac with white plaques. (D) Multifocal hepatic white plaques (circle). (E) Large space-occupying mass originating from the left ovary, accompanied by multifocal white plaques on the surface of the liver. (F) Two enlarged, yellow ovaries were noted to be firmly adhered to the liver.
Histopathology of Malignant Iridophoroma in Leopard Geckos. (A) Dermis and subcutis at the head skin are expanded by neoplastic cells. These cells are also found in the marrow cavity (arrow). (B) High magnification of the skin mass showing sheets of pleomorphic, variously pigmented neoplastic cells supported by fine fibrovascular stroma. (C) Same view as B but under polarized light, showing the various degrees of birefringent, intracytoplasmic, or extracellular granules of the tumor. (D) Tumor mass in the liver. (E) Same view as D but under polarized light, showing the birefringent granules of the tumor. Resident melanomacrophages, which are normally present in the liver of reptiles, do not have birefringent granules. (F) Tumor infiltration in the ovary. (G) Tumor infiltration in the iris of the eye. (H) Tumor at the meninges of the brain. Inset: birefringence of the tumor in the meninges (box).
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