Johannes Junginger1, Florian Geburek2, Muhammad Akram Khan1, Gundi Müller3, Achim D Gruber4, Marion Hewicker-Trautwein1. 1. Department of Pathology, University of Veterinary Medicine, Bünteweg 17, D-30559, Hannover, Germany. 2. Clinic for Horses, University of Veterinary Medicine, Bünteweg 9, D-30559, Hannover, Germany. 3. Non-clinical safety, Global early development, Merck KGaA, Frankfurter Straße 250, D-64293, Darmstadt, Germany. 4. Department of Veterinary Pathology, Freie Universität Berlin, Robert-von-Ostertag-Str. 15, D-14163, Berlin, Germany.
Abstract
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. OBJECTIVES: To describe a new variant of equine cutaneous maculopapular mastocytosis lacking systemic involvement. ANIMALS: 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 AND CLINICAL IMPORTANCE: 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.
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 humancutaneous mastocytosis, including urticaria pigmentosa and solitary mastocytoma, are usually restricted to the skin. OBJECTIVES: To describe a new variant of equinecutaneous maculopapular mastocytosis lacking systemic involvement. ANIMALS: 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 AND CLINICAL IMPORTANCE: The case presented here fulfils the criteria of equinecutaneous 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.