Pulse - June 2022 - 13

PRACTICAL PATHOLOGY
Cutaneous Lymphocytosis
(Pseudolymphoma) in a Cat
Farshid Shahriar DVM, PhD, DACVP - Lore Laboratory, 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cutaneous lymphocytosis /(pseudolymphoma outdated term in the literature) from nonepitheliotropic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.
Figure 1
Figure 2
Figure 3
PULSE
JUNE 2022
13

Pulse - June 2022

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