Pulse - April 2023 - 9

PRACTICAL PATHOLOGY
Cutaneous Lymphocytosis
(Pseudolymphoma) in a Cat
Farshid Shahriar DVM, PhD, Dipl ACVP - Lab For Pets, Tustin, CA
Medical history and clinical findings:
Biopsies from a dermal lesion of a 6 year-old, female-spayed cat was submitted for histopathology.
Biopsy was from a raised grwoth. Histopathology was performed.
Histopathologic findings:
Histopathology shows evidence of a nodular skin lesion with a diffuse to nodular unencapsulated
dermal and subcutaneous infiltrate of a monomorphic population of uniform small blue cells
with features of lymphoid cells with small round nuclei with clumped chromatin, visible nucleoli
and little amphophilic cytoplasm without distinct cytoplasmic margins (Fig. 1, 2). There are 0-1
mitotic figures/10 hpf with no germinal centers typically noted with cutaneous lymphocytosis/
pseudolymphoma and there is no exocytosis of small lymphoid cells into the epidermis or follicular
epithelium (Fig.3) or the apocrine sweat glands so there is no evidence of epitheliotropism to
implicate cutaneous epitheliotropic lymphoma. There is a uniformly spaced fibrovascular stromal
component with this lymphoproliferative infiltrative lesion which is likely to be pre existing. No
organisms, viral inclusions, vacuoles, granules, eosinophils, flame figures, lymphoid follicles, germinal
centers, granulomas, multinucleate giant cells or foreign bodies are seen.
Diagnosis:
Diagnosis of a cutaneous small blue cell neoplasm with features of a lymphoproliferative round
cell neoplasm was made.
Discussion:
Immunohistochemistry and PCR techniques for clonality are advised to differentiate cutaneous
lymphocytosis /(pseudolymphoma outdated term in the literature) from nonepitheliotropic lymphoma
which may develop in lesions with chronic antigenic stimulation of lymphocytes in a variety
of species or other possible small blue cell types but the lack of mitotic figures makes other
small blue cell tumor types less likely. There are no germinal centers or other intermixed cell types
typically noted with pseudolymphoma and histiocytic lesions. Some consider such lesions to be reactive
ones that often evolve into a low-grade indolent lymphoma and many consider such lesions
to be low grade small lymphocytic cell type lymphoma. In cats, cutaneous lymphocytosis may be
associated with a drug reaction (e.g. Phenobarbital, methimazole, injection sites, etc...), FELV,
FIV, herpes virus, Borrelia burgdorferi, Bartonella henselae; contact allergens or foreign bodies (e.g.,
arthropod bites, etc...). Pseudolymphoma (an outdated term in the literature) has been reported
in a Blue and Gold macaw and subcutaneous lymphoma has been reported in cockatoos. Marek's
Disease Virus and Reticuloendotheliosis Virus are of concern in poultry with lymphocytic skin
lesions with features similar to this one. In dogs rarely cutaneous lymphocytosis lesions have been
suggested to be a delayed type hypersensitivity reaction in response to tick bites or possibly Bartonellosis
or other antigenic stimuli or a drug reaction, etc. Evaluate for possible systemic diseases
(e.g. Vector borne infections, GI, hepatic, pancreatic disease, diabetes mellitus, etc...), drugs, toxins,
allergens, tumors at a nearby or distant site, is warranted. P
Figure 2
Figure 1
Figure 3
PULSE
APRIL 2023
9

Pulse - April 2023

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