A 6-year-old male German Shepherd dog died unexpectedly and the body was submitted to the AHL for postmortem examination. The dog had been alone in a home at the time of death, and was found in the proximity of the propane furnace used to heat the home. There was no indication of distress prior to death. The dog had been healthy prior to this time. The owners were concerned about carbon monoxide (CO) poisoning as the cause of death, due to recent mechanical issues with the furnace.
No significant gross lesions were identified during autopsy. Heart blood was collected in EDTA and heparin for CO analysis at an external laboratory. Blood analysis by gas chromatography / mass spectrometry (GC/MS) identified 66% saturation of hemoglobin by CO (carboxy-hemoglobin, COHb), confirming CO toxicosis as the cause of the dog’s death. In humans, normal COHb levels in blood can reportedly reach 4% (8% in smokers). Clinical signs are identified in humans with COHb levels over 10%, and levels greater than 40% generally result in death.
CO binds to hemoglobin with much greater affinity (>200X) than does oxygen. Resulting displacement of oxygen from hemoglobin and defective release of residual bound oxygen leads to tissue hypoxia. Neurologic and cardiorespiratory signs may be evident in animals with CO poisoning. No specific gross or histologic lesions are identified in acute fatalities due to carbon monoxide poisoning, and definitive diagnosis relies on determination of COHb levels in blood. Dogs with sublethal CO poisoning may demonstrate neuronal necrosis in anatomically specific sites in brain (globus pallidus, substantia nigra, cerebellum, hippocampus), or a more delayed form of toxicity associated with myelin degeneration in deep white matter tracts in brain. Both tissue hypoxia and hypotension likely contribute to these lesions.
Histologic lesions in this dog were limited to a few foci of acute myocardial necrosis, compatible with terminal myocardial hypoxia due to CO poisoning.
Cutaneous smooth muscle tumors are rare in ferrets, but have been reported in the literature as having arisen from the arrector pili muscle of the hair follicles of the skin (termed piloleiomyomas or piloleiomyosarcomas). Piloleiomyosarcoma has been designated as malignant based on nuclear pleomorphism but typically is well-demarcated and amenable to surgical excision. A recurrent variant has been described as “multiple progressive piloleiomyoma”.
Recently, AHL pathologists have examined 2 similar tumors in ferrets. A mature male neutered ferret had a focal roughly 1 cm diameter nodule above one of its eyes. Histologically, it was a well-circumscribed and expansile dermal mass composed of large strap-shaped cells with fibrillar cytoplasm, extensive anisokaryosis and binucleation, but with a low mitotic index. This mass was closely apposed to an arrector pili muscle within the dermis. The second animal was submitted through the Department of Pathobiology, and was seen in consultation. This mass was 1.5 cm diameter, 2 cm from the base of the tail, and had similar cytologic features as the first but with 1-2 mitotic figures per 400X field. For both of these tumors, immunohistochemistry was performed and demonstrated strong cytoplasmic staining for vimentin and both smooth-muscle and pan-muscle actin, a pattern consistent with a smooth muscle pattern of differentiation.
The descriptive terminology for such tumors is contentious. The well-circumscribed phenotype of these masses suggests a benign biological growth habit which, in spite of nuclear pleomorphism, would make the terms leiomyoma or piloleiomyoma most appropriate; however, the pleomorphism present in each, coupled with the mitotic index in the second mass, compels some pathologists to diagnose these as sarcomas. These were both recent submissions, and follow-up is ongoing to determine whether these are individual single benign tumors, or whether these animals might have a predisposition to multiple such masses. The fact that these masses were individual and localized suggests that these are likely individual masses and unlikely to represent the syndrome described as multiple progressive piloleiomyomas, in which the lesions formed cord-like skin plaques.
The current literature strongly suggests that such solitary masses are likely cured by complete excision regardless of pleomorphism and mitotic index, making leiomyoma or piloleiomyoma a more appropriate designation for similar well-defined dermal tumors.