History

A 3-year-old 10-kg (22-lb) male French Bulldog was evaluated by a referring veterinarian because of a cutaneous nodule on the forelimb close to the shoulder joint region, which was removed when the dog was anesthetized for a bilateral orchiectomy procedure. No histologic examination of the tissue was performed. Two months later, the dog developed 15 cutaneous nodules that were scattered over the dorsum and head. At that time, results of abdominal ultrasonography, a CBC, and serum biochemical analysis were unremarkable. No further diagnostic tests were performed. The dog received cephalexin^a (20 mg/kg [9.1 mg/lb], PO, q 12 h) and cetirizine hydrochloride^b (1 mg/kg [0.45 mg/lb], PO, q 24 h) for 7 days. Three months after removal of the first nodule, the cutaneous lesions persisted, and the dog was referred for examination at the Veterinary Hospital at Fluminense Federal University.

Clinical Findings

On physical examination, the dog had multifocal, pruritic, and erythematous skin nodules and plaques of variable size located on the dorsum and head, which were too numerous to count. There were coalescing erythematous plaques and nodules on the ventral aspect of the abdomen (Figure 1). Some of the lesions were ulcerated. The skin lesions had progressively appeared over a period of approximately 3 months. Mandibular and inguinal lymph nodes were enlarged. No other gross abnormalities were observed, and the dog's body condition score (3/5) was considered ideal.

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Photographs of a 3-year-old neutered male French Bulldog with multifocal skin lesions that developed over a period of several months. A—Notice the variably sized and ulcerated nodules on the head. Inset—Nonulcerated nodules are present on the chin. B—There are coalescing erythematous plaques and nodules on the ventral aspect of the abdomen.

Citation: Journal of the American Veterinary Medical Association 256, 5; 10.2460/javma.256.5.559

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Formulate differential diagnoses from the history, clinical findings, and Figure 1—then turn the page→

Cytologic Findings

Fine-needle aspirate specimens were obtained from an enlarged inguinal lymph node and multiple skin nodules for cytologic evaluation. Smear preparations were stained with Romanowsky-Giemsa stain. The lymph node and skin nodule smears contained large numbers of round cells with abundant clear cytoplasm, anisocytosis, anisokaryosis, and irregular vacuolization. Coarse chromatin, atypical mitotic figures, and multinucleated cells were occasionally observed (Figure 2).

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Photomicrographs of one of several fine-needle aspirate specimens obtained from multiple skin nodules from the dog in Figure 1. A—The nodules contained large numbers of round cells with abundant clear cytoplasm. Aqueous Romanowsky-Giemsa stain; bar = 20 μm. B—The round cells have anisocytosis, anisokaryosis, and irregular vacuolization. Aqueous Romanowsky-Giemsa stain; bar = 10 μm. C—Some round cell nuclei have coarse chromatin, and atypical mitotic figures (arrow) are occasionally seen. Aqueous Romanowsky-Giemsa stain; bar = 20 μm. D—Some multinucleated cells (arrowhead) are present. Aqueous Romanowsky-Giemsa stain; bar = 20 μm.

Citation: Journal of the American Veterinary Medical Association 256, 5; 10.2460/javma.256.5.559

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Excisional biopsy specimens were obtained from multiple cutaneous nodules. Tissues were fixed in neutral-buffered 10% formalin and submitted for histologic analysis.^c Because of the large number and extent of the lesions, complete surgical removal was not feasible. The dog was treated with cyclosporine^d (5 mg/kg [2.3 mg/lb], PO, q 24 h) for 15 days without clinical improvement; treatment was discontinued at the owner's request.

Four months after removal of the first nodule, the dog developed signs of depression, anorexia, and hypothermia. Large ulcerated skin masses had spread throughout the body, affecting mostly the face, limbs, and ventrum. Given the deterioration of the dog's clinical condition, euthanasia (by IV injection of euthanasia solution) was elected. Necropsy was declined by the owner.

Histopathologic Findings

Tissue specimens collected for histologic examination were routinely processed and stained with H&E stain. Histopathologic features included a densely cellular infiltrate of neoplastic round cells centered on the superficial dermis. The neoplastic cells had an intimate association with the overlying epidermis, and groups of tumor cells were seen within the epithelium. The cytomorphologic features of neoplastic cells and histopathologic findings were compatible with a histiocytic proliferative disease.

Immunohistochemical Analyses

Immunohistochemical analyses^c of a cutaneous nodule were performed. All neoplastic cells reacted strongly with antibodies against CD18 but were unreactive with antibodies against CD3 and E-cadherin. Unfortunately, more comprehensive immunophenotyping of the lesions was not performed because of a lack of frozen tissue samples.

Morphologic Diagnosis and Case Summary

Morphologic diagnosis: severe, chronic, diffuse neoplasm of histiocytic origin on the superficial dermis.

Case summary: presumptive Langerhans cell histiocytosis (LCH) in a dog.

Comments

Histiocyte is an overarching term to describe cells that differentiate from CD34+ stem cell precursors in the bone marrow into macrophages and several dendritic cell (DC) lineages. Dendritic cells are the most potent antigen-presenting cells for induction of immune responses in naïve T cells.¹

The most well-defined DCs in dogs are those in the skin, namely epidermal DCs (or Langerhans cells) and dermal DCs (part of the interstitial DC lineage).^2–4 Langerhans cells are found not only within the epithelium of the skin but also in the alimentary, respiratory, and reproductive tracts.⁵ Most canine histiocytic diseases involve proliferations of Langerhans cells or DCs of interstitial lineage.¹

Primary histiocytic dermatoses are a group of skin disorders in which histiocytic cells predominate histologically in the absence of any known proliferative stimuli such as infectious agents, foreign bodies, and metabolic products.⁶ There are at least 4 well-defined histiocytic proliferative diseases in dogs: cutaneous histiocytoma, LCH, cutaneous or systemic histiocytosis, and histiocytic sarcoma or malignant histiocytosis. These diseases are challenging to diagnose because, in some cases, it may be difficult to differentiate them from granulomatous, reactive inflammatory diseases or from lymphoproliferative diseases through examination of paraffin-embedded sections.⁷

Canine cutaneous histiocytoma is a common, benign cutaneous neoplasm that originates from Langerhans cells and regresses spontaneously.⁸ Cutaneous histiocytoma develops most frequently in dogs < 3 years old, although it occasionally affects older dogs.⁷ The neoplasm is usually a fast-growing, nonpruritic, painless, solitary mass⁷ that appears as a small, firm, dome- or button-shaped dermal mass on the head, pinnae, neck, or limbs.⁸ Langerhans cell histiocytosis develops as multiple cutaneous histiocytomas at the same or distant sites with possible involvement of lymph nodes and internal organs.⁷ Langerhans cell histiocytosis is considered a rare form of canine cutaneous histiocytoma that affects < 1% of dogs with histiocytomas.¹ In dogs and cats with LCH, the skin is invariably involved; even when systemic disease eventuates, the skin is always the initial site of origin.¹ For human patients, data suggest a genetic component in the development of LCH.⁹ In dogs, the etiopathogenesis of LCH remains unknown.²

As seen in the case described in the present report, dogs with LCH have extensive skin involvement characterized by cutaneous lesions ranging from nodules to masses that elevate the epidermis and may be accompanied by redness, alopecia, and ulceration. The lesions are also described as erythematous papules, plaques, and crusts.⁶ Spontaneous remission is possible in animals with cutaneous LCH and occurs in approximately half of the cases, unless lymph node involvement is present.¹⁰

Cytologic features of LCH do not differ markedly from those of cutaneous histiocytoma and include the presence of round cells with clear and abundant cytoplasm and a nucleus that may be round to oval, indented, or complexly folded. Occasional multinucleated histiocytes may be observed. Other cytologic atypia, such as anisokaryosis and hyperchromatic nuclei, are unusual findings.¹

Histopathologic characteristics of LCH lesions include extensive regional cutaneous infiltration by histiocytes, which otherwise resemble those in histiocytomas.⁷ Furthermore, there is homogeneous accumulation of histiocytic cells in the dermis and subcutis and intraepithelial infiltration by such cells. These histiocytic cells are ovoid with abundant pale eosinophilic cytoplasm and an oval, round, folded, or pleomorphic nucleus with 1 or sometimes 2 small nucleoli that stain well. Mitoses and atypia are not readily observed; however, in cases of aggressive disease, such as that described in the present report, the lesions have a higher degree of cytologic atypia but maintain tropism for the epidermis. Histiocytes may have more anisokaryosis and multinucleated cells than is typical of cells in solitary histiocytomas.^1,6 For the dog of the present report, the criteria of malignancy, such as coarse chromatin, multinucleation, and rare atypical mitotic figures, were apparent in few cells. The limited detection of these characteristics along with the epitheliotropic nature of the tumor cells made a diagnosis of malignant histiocytosis very unlikely.

In cases of cutaneous and systemic histiocytosis, 1 of the 4 histiocytic proliferative diseases, the lesions are dominated by activated dermal interstitial DCs and T cells, both of which frequently infiltrate the walls of dermal vessels and can lead to lymphohistiocytic vasculitis. The lesions usually arise from the deep dermis and therefore have a so-called bottom-heavy topography rather than the top-heavy topography of histiocytomas.^1,2 Lymphohistiocytic vasculitis was not evident in the case described in the present report.

Results of immunohistochemical analysis are useful for distinguishing histiocytic disease from other disorders such as lymphoma or other round cell tumors. Canine epidermal Langerhans cells are characterized by expression of CD1a, CD1b, CD1c, major histocompatibility complex class II, CD11c, and E-cadherin, all of which can be detected by immunohistochemical analyses of snap-frozen sections; largely, such analyses could not be performed in this case because of a lack of frozen tissue. Nevertheless, immunohistochemical analysis for E-cadherin can also be performed on formalin-fixed paraffin sections.³ Although E-cadherin expression by neoplastic cells is suggestive of Langerhans cell origin, the lack of E-cadherin expression by the neoplastic cells in the case described in the present report does not disprove a Langerhans cell origin.¹

In formalin-fixed paraffin-embedded sections, histiocytomas can be readily distinguished from cutaneous lymphomas by intense CD18 expression and lack of CD3 and CD79a expression by tumor histiocytes. A lack of CD3 and CD79a expression rules out T-cell and B-cell proliferative disorders, respectively.³ Immunohistochemical analyses for CD3 and CD18 but not CD79a were performed in the case described in the present report, and the findings ruled out epitheliotropic T-cell lymphoma.

Although some histiocytic proliferative diseases have a familial association, especially in Bernese Mountain Dogs,⁸ LCH does not seem to have a breed predisposition. Unpublished data suggest that multiple histiocytomas develop more often in Chinese Shar-Peis (approx 20% of cases); however, they can develop in any breed of dog.¹⁰ To the authors’ knowledge, this is the first report of presumptive LCH in a French Bulldog.

Treatment options for dogs with histiocytic proliferative diseases include excision of the lesions and administration of immunosuppressive and immunomodulatory medications and chemotherapy.¹¹ The results vary greatly depending on the type of disease. In dogs with LCH, treatment with prednisolone has not been associated with good outcomes. However, the use of immunomodulatory drugs, such as griseofulvin, seems to be more effective in the short-term control of clinical signs.⁶ For the dog of the present report, treatment with an immunomodulatory drug (cyclosporine) for 15 days was not successful. However, pharmacokinetic analyses have revealed that the time to steady state (ie, the time to evaluate any therapeutic response to treatment) for cyclosporine ranges from negligible (ie, there is no steady state) to 18 to 25 days or more,¹² and it is possible that the period of treatment for the dog of the present report was insufficient to achieve a clinical response. It should be noted that as described previously,^6,10 the presence of multiple histiocytomas and lymph node involvement correlates with a poor prognosis and usually results in euthanasia of the affected dog.