Page 171 - Differential Diagnosis in Small Animal Cytology, The Skin and Subcutis

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Feline progressive dendritic cell histiocytosis (FPH)
VetBooks.ir Histiocytic disease arising from interstitial dendritic cells.

Clinical features

• Disease of middle-aged to older cats (7–17 years).
• Presenting either as a solitary skin nodule or multiple papules, nodules or plaques.
Lesions measure up to 1.5 cm in diameter; they are firm, often alopecic, non-pruritic
and non-painful. They may wax and wane, but spontaneous regression does not
occur. Involvement of lymph nodes and internal organs can be observed.
• Preferred locations include the head, lower extremities and trunk.
• The initial clinical course is indolent and the neoplasm behaves like a low-grade dis-
ease. However, long-term prognosis is poor, as the disease is progressive.

Cytological features
• The cellularity is variable, from low to high.
• Background: clear to lightly basophilic, variably haemodiluted.
• Neoplastic cells are round to polygonal, rarely spindloid, with poorly defined cytoplasmic
borders. They exfoliate either individually or in poorly cohesive groups.
• Nuclei are oval to reniform, occasionally indented, paracentral to eccentric, with finely stippled to
reticular chromatin. A single, round and prominent nucleolus is occasionally visible.
• The cytoplasm is moderate to abundant and lightly basophilic. It may contain rare clear
vacuoles and, at times, it may appear wispy and paler at the outer edges.
• Anisocytosis and anisokaryosis are variable, generally moderate to marked. Binucleation,
multinucleation and rare mitotic figures can be found.
• Low numbers of small lymphocytes, mast cells and other inflammatory cells are not
uncommon.

Pearls and Pitfalls
Presumptive diagnosis can be attempted by assessment of the cytomorphology in con-
junction with the clinical presentation. Definitive confirmation of the dendritic lineage
requires immunophenotyping and this can be obtained specifically by demonstrating CD1
expression on cytological or histological preparations.