Page 1505 - Clinical Small Animal Internal Medicine

164 Canine Sterile Papular and Nodular Skin Diseases 1443

followed by Rottweilers (4/26), and golden and Labrador in the pathogenesis of canine reactive histiocytosis.
VetBooks.ir retrievers (3/26). The age at the time of diagnosis varies Ocular lesions may be more difficult to treat and often
require the use of ophthalmic ciclosporin preparations.
from 1 to 9 years. Males seem to be more frequently
affected in Bernese mountain dogs. No sex predisposi-
agents has shown poor response.
tion was observed in other breeds. The use of high doses of glucocorticoids and cytotoxic
Clinical Signs Prognosis
Systemic histiocytosis differs from CH in the extent of The prognosis is guarded; the clinical course waxes and
lesions present and the multiorgan involvement. Lesions wanes but it is usually prolonged. Most cases are eutha-
affect the skin, with high prevalence for mucocutaneous nized due to relapse of clinical signs or poor response to
junctions; other organs commonly involved include the therapy.
nasal cavity, eyes, spleen, lymph nodes and testicular tis-
sue. Bone marrow, liver, lungs, and gingiva can also be Histiocytic Sarcoma Complex
affected. In a recent study, 2/26 dogs had hypercalcemia. Previously known as malignant histiocytosis, this com-
The clinical signs vary depending on the organs affected plex includes localized and disseminated histiocytic sar-
and extension of the lesions. Anorexia, weight loss, con- coma (HS). Histiocytic sarcoma is a highly aggressive
junctivitis, and stertorous respiration are commonly neoplasm. It may develop as a localized tumor or a
seen. The disease waxes and wanes and dogs are asymp- widely disseminated disease; animals with initially local-
tomatic between clinical episodes. The clinical episodes ized disease often develop metastasis. The disease is
can increase in severity and respond less effectively to characterized by infiltration of neoplastic proliferation
therapy with chronicity. of cells of the histiocytic lineage, including dendritic
antigen‐presenting cells and macrophages. The pres-
Diagnosis ence of macrophages has been documented only in
Clinical differential diagnoses include neoplasia, infec- cases of hemophagocytic HS, in which the histiocytes
tious and sterile granulomas, cutaneous histiocytosis, are markedly erythrophagocytic. Histiocytic sarcoma is
and cutaneous sterile granuloma and pyogranuloma syn- highly breed specific, with Bernese mountain dogs,
drome. The diagnosis is based on history, clinical signs, Rottweilers, and flat‐coated and golden retrievers hav-
cytology, histopathology, and ruling out infectious causes. ing a high prevalence. Immunohistochemistry plays an
Cytologic findings are similar to CH, consisting mainly important role in differentiating histiocytic tumors from
of large numbers of histiocytes, with occasional bi‐ or other neoplasias with similar histopathologic findings
multinucleated giant cells. Histopathologic findings are such as lymphoma, poorly differentiated mast cell
identical to those observed with CH, composed of multi- tumors, and malignant fibrous histiocytoma.
focal nodular infiltrate affecting the deep dermis and
subcutaneous tissue. The cellular infiltrate consists Pathogenesis
mainly of histiocytes, lymphocytes, and neutrophils. The Histiocytic sarcomas are characterized by localized
infiltrate is angiocentric and may invade the blood ves- or disseminated infiltration of malignant histiocytes.
sels, causing destruction of the vascular wall, thrombo- Expected immunohistochemical expression pattern
sis, and ischemic necrosis. Invasion of the blood vessel for HS in snap‐frozen tissue samples is CD1+, CD4‐,
wall has been observed more consistently in cases of SH. CD11c+, CD11d‐, MHC II+, ICAM1+, Thy ‐1+/‐.
The infiltrating histiocytes express CD1+, CD11c+, Hemophagocytic HS expresses MHC II, beta‐2 integrin,
MHC II+, CD4+, and Thy‐1+ (CD90), consistent with and CD11d. The disease is familial in Bernese mountain
activated dermal dendritic cells. dogs in which an oligogenic mode of transmission has
been proposed.
Therapy
The clinical signs wax and wane, and some dogs can Signalment
undergo long periods of remission, but most cases require Histiocytic sarcoma affects mainly Bernese mountain
long‐term immunomodulatory therapy. The experimen- dogs, Rottweilers, flat‐coated and golden retrievers with
tal use of thymosin, which modulates T lymphocyte a median age at presentation of 8 years. The tumor has
effector and regulatory function, has shown promising been found to have a male predisposition in Bernese
results; however, further use of this treatment has not mountain dogs and flat‐coated retrievers.
been documented. Good response has been seen with
leflunomide and ciclosporin, both of which have an Clinical Signs
inhibitory effect on T lymphocytes. The good response to Localized HS is reported to be most common in the
these drugs suggests an important role of T lymphocytes bone, appendicular joints, and skin. Distant metastasis