384 DISEASES/DISORDERS
Periadnexal multinodular granulomatous dermatitis: benign, well-demarcated cuta-
neous nodules, commonly on the muzzle and may affect the eye; histologically dis-
tinct granulomas and variable numbers of inflammatory cells; may be indistinguish-
able from cutaneous histiocytosis.Granulomatous infectious diseases (e.g., nocardiosis, actinomycosis, and mycotic dis-
eases): may have nodular pulmonary opacities.
Hemophagocytic syndrome (histiocytosis): benign histiocytic proliferation secondary
to infectious, neoplastic, or metabolic disease; can affect bone marrow, lymph nodes,
liver, and spleen; causes cytopenia of at least two cell lines.Anaplastic carcinoma or sarcoma: histopathologic findings in dogs with histiocytosis
may indicate a poorly differentiated tumor; immunostaining for tissue-specific mark-
ers will differentiate.DIAGNOSTICS
Histiocytoma: no abnormalities on routine diagnostic tests.
Reactive histiocytosis: anemia (regenerative or nonregenerative), thrombocytopenia,
monocytosis, lymphopenia.
Histiocytic sarcoma: anemia (regenerative or nonregenerative), thrombocytope-
nia, monocytosis, lymphopenia, pancytopenia, hypoalbuminemia, elevated liver
enzymes.Biochemistry results reflect the degree of organ involvement; hypercalcemia reported.
Serum ferritin: may be a tumor marker for malignant histiocytosis; one affected
dog had very high serum ferritin concentration, suggesting secretion by neoplastic
mononuclear phagocytes.Thoracic radiographs: well-defined, nodular pulmonary opacities (single or multi-
ple), pleural effusion, lung lobe consolidation, diffuse interstitial infiltrates, medi-
astinal masses, and sternal and bronchial lymphadenomegaly.Abdominal radiographs: hepatomegaly, splenomegaly, abdominal effusion.
Biopsy of affected organs and/or lymph nodes.
Fine-needle aspirate cytology of histiocytoma: pleomorphic round cells with
basophilic cytoplasm and round to slightly indented nuclei (Figure 25.11)
Cytologic examination of bone marrow aspirate or biopsy reveals histiocytic infiltra-
tion.
Immunohistochemistry: results of cytologic/histologic examinations not always
definitive; cytochemical staining useful in determining the histiocytic origin of the
cells.Histopathologic Findings
Histiocytoma:
Trophism of histiocytes towards the dermis and epidermis may result in nests of
cells within the dermis; similar in appearance to epitheliotropic lymphoma.
Diffuse dermal and subcutaneous pleocellular histiocytic infiltrate.