Cutaneous form of maculopapular mastocytosis in a foal.
BACKGROUND
Cutaneous mastocytosis is a rare benign disease occurring in domestic animals and humans. In previous reports, dermal findings in foals were accompanied by systemic mast cell infiltrations, whereas lesions in human cutaneous mastocytosis, including urticaria pigmentosa and solitary mastocytoma, are usually restricted to the skin.


OBJECTIVE
To describe a new variant of equine cutaneous maculopapular mastocytosis lacking systemic involvement.


METHODS
A 2.5-month-old warmblood foal with multiple skin nodules since birth.


METHODS
Clinical examination (including haematology, fine needle biopsy and thoracic radiographs), postmortem examination, histopathology and immunohistochemistry.


RESULTS
Clinical examination showed 41 skin nodules that contained numerous mast cells as detected by cytology. Macroscopic examination at postmortem examination revealed intradermal circumscribed lesions ranging from 2 to 5 cm in diameter. Histologically, they were composed of well differentiated mast cells with metachromatic granules stained with toluidine blue accompanied by many eosinophils. Immunohistochemically, mast cells had mast cell growth factor receptor c-KIT predominating at the cell surface and intracytoplasmic expression of tryptase. In other organs similar mast cell infiltrations were not detected.


CONCLUSIONS
The case presented here fulfils the criteria of equine cutaneous maculopapular mastocytosis (ECMM), representing a rare entity in foals that is reported to be associated with spontaneous regression, although the long-term prognosis is not known. Unlike in previous reports, lesions described here were restricted to the skin. This may imply that ECMM is primarily a dermal disease sharing similarities with urticaria pigmentosa in young children.
Department of Pathology, University of Veterinary Medicine, Bünteweg 17, D-30559, Hannover, Germany.
Johannes
J
Junginger
Clinic for Horses, University of Veterinary Medicine, Bünteweg 9, D-30559, Hannover, Germany.
Florian
F
Geburek
Department of Pathology, University of Veterinary Medicine, Bünteweg 17, D-30559, Hannover, Germany.
Muhammad Akram
MA
Khan
Non-clinical safety, Global early development, Merck KGaA, Frankfurter Straße 250, D-64293, Darmstadt, Germany.
Gundi
G
Müller
Department of Veterinary Pathology, Freie Universität Berlin, Robert-von-Ostertag-Str. 15, D-14163, Berlin, Germany.
Achim D
AD
Gruber
Department of Pathology, University of Veterinary Medicine, Bünteweg 17, D-30559, Hannover, Germany.
Marion
M
Hewicker-Trautwein