Diagnosis disagreement in “Pathology in Practice”
In a recent Pathology in Practice article,1 the authors describe a 1-year-old Quarter Horse colt with a 6-month history of nasal discharge and respiratory noise. Clinical and radiographic findings indicated a mass filling the left nasal passage and paranasal sinuses. The authors wrote that, at necropsy, a multilobulated bony mass was found and that histologic findings were consistent with a poorly productive, osteoblastic osteosarcoma. They also state that osteosarcomas “generally consist of proliferating lamellar bone and intratrabecular fatty and hematopoietic marrow.” However, I believe this description more accurately describes benign bone proliferation as one would see with an osteoma or osseous metaplasia.
I question whether the morphologic diagnosis in this case was correct. To classify this tumor as osteoblastic, the cells should have been polygonal or sail-shaped, rather than spindle-shaped, as indicated in the report. I believe that fibroblastic osteosarcoma would have been a better diagnosis, as this type of osteosarcoma has regions of spindle cells, produces collagenous matrix that is not osteoid, and has fewer mitoses. However, this still would not be the best diagnosis because even with fibroblastic osteosarcomas, there are regions of osteoblastic differentiation and production of osteoid.
The long time course of clinical signs (nasal discharge and respiratory noise), age of the horse (6 months at the time of onset and 1 year at the time of diagnosis), and location of the tumor (caudal part of the left nasal passage and paranasal sinuses) should, in my opinion, have prompted a discussion of benign but locally destructive tumors such as odontogenic tumors, ossifying fibromas, and osteomas.2–4
The photomicrographs that accompany the article appear to demonstrate a slowly expanding mesenchymal neoplasm compatible with a low-grade sarcoma, ossifying fibroma, or odontogenic tumor. Panel A of Figure 2 shows the tumor approaching the respiratory mucosa, and the tumor is bordered at the leading edge by a rim of reactive woven bone partially effaced by the expanding tumor. In panel B of that figure, the arrowhead indicates poorly defined matrix, with no indication of its composition. No mention is made of special staining to rule out myxomatous stroma or chondroid matrix or to demonstrate fibrillar collagenous matrix. The interpretation of osteoid should be reserved for fibrillar collagenous matrix (with or without mineralization), with low proteoglycan content, that often contains entrapped cells. Panel C of Figure 2 identifies a group of cells adjacent to a woven bone spicule as an osteoclast. However, the regular arrangement of nuclei and the absence of bone resorption (ie, the lack of Howship lacunae) suggest as an alternative interpretation that this is an odontogenic rest. The cells could have been differentiated from an osteoclast by immunohistochemical staining for pancytokeratin and vimentin. Additionally, the presence of osteoclasts in the nasal cavity, turbinates, or sinuses is not unusual, as there is often reactive bone and osteoclastic remodeling in association with chronic inflammatory disease and neoplasia.
This is an interesting case worthy of further diagnostic investigation. Additional histologic sections may have helped reveal regions more convincing of an osteosarcoma of fibroblastic, osteoblastic, or mixed type. Until then, the diagnosis should remain open, and additional differential diagnoses of ossifying fibroma, low-grade fibrosarcoma, and odontogenic fibroma should be considered.
Brian G. Caserto, dvm
VetPath Services
Stone Ridge, NY
1. Cesar FBJoiner KSAlbanese V, et al. Pathology in practice. J Am Vet Med Assoc 2016;248:773–775.
2. Fjordbakk CTPekarkova MDolvik NI, et al. Maxillary odontogenic myxoma in young horses: six cases (2003–2011). Equine Vet Educ 2015;27:569–573.
3. Head KWDixon PM. Equine nasal and paranasal sinus tumours. Part 1: review of the literature and tumour classification. Vet J 1999;157:261–279.
4. Roberts MCGroenendyk SKelly WR. Ameloblastic odontoma in a foal. Equine Vet J 1978;10:91–93.
More research needed for Munchausen by proxy and pets
Originally defined by Meadow,1 Munchausen by proxy (MBP) is a complex disorder that involves the purposeful fabrication or infliction of an illness or injury in a human or animal by a caregiver for the purpose of gaining attention from others, particularly in the medical or veterinary field. Most of the research associated with MBP focuses on cases in which a child is the victim; however, recent evidence suggests that this disorder can involve pets. The latter finding is not particularly surprising, given that many owners view their pets as members of the family and that pets are wholly dependent on their owners for care. Cases of MBP have been identified not only through face-to-face interactions, but also through the Internet (eg, online blogs or discussion forums), with this variation referred to as MBP by Internet.2 In these situations, individuals spread false claims of illness or injury via social media, potentially misleading hundreds or thousands of other people.
To date, all animal-related cases of MBP reported in the professional literature have, to our knowledge, involved victimization of dogs or cats. For example, Feldman3 described a case of suspected MBP involving a dog that starved to death despite multiple visits to a veterinarian, Meadow4 briefly mentioned four cases in which pets died under unusual circumstances representative of suspected MBP, and Munro and Thursfield,5 in a survey of 448 nonaccidental injuries involving dogs and cats, reported nine cases of MBP.
However, we believe that MBP could affect other pets that are commonly kept, such as horses. It has previously been estimated that there are 4.8 million horses in the United States,6 and owners have been noted to closely bond with their horses.7 In this regard, one of the authors (MDF) is aware of a case involving fabricated or induced Cushing syndrome in a horse.
There is a notable lack of research on MBP involving pets, particularly research on the signs of MBP, the impact of MBP on pets and family members, and the challenges involved in proving such cases to the local authorities. As additional information is gathered, we believe that evidence-based guidelines should be developed to help veterinarians and their staff members identify and intervene in suspected or confirmed cases of MBP involving the victimization of animals.
James A. Oxley, bsc, mres
Romford, Essex, England
Marc D. Feldman, md
Department of Psychiatry and Behavioral Medicine
University of Alabama
Tuscaloosa, Ala
1. Meadow R. Munchausen syndrome by proxy. The hinterland of child abuse. Lancet 1977;2(8033):343–345.
2. McCulloch VFeldman MD. Munchausen by proxy by Internet. Child Abuse Neglect 2011;35:965–966.
3. Feldman MD. Canine variant of factitious disorder by proxy. Am J Psychiatry 1997;152:1316–1317.
4. Meadow R. Munchausen syndrome by proxy abuse perpetrated by men. Arch Dis Child 1998;78:210–216.
5. Munro HMCThursfield MV. Battered pets: Munchausen syndrome by proxy (factitious illness by proxy). J Small Anim Pract 2001;42:385–389.
6. AVMA. US pet ownership and demographics sourcebook (2012). Schaumburg, Ill: AVMA, 2012.
7. Hausberger MRoche HHenry S, et al. A review of the human-horse relationship. Appl Anim Behav Sci 2008;109:1–24.
