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Small Animal Section: No. 6
SPLENOMEGALY IN THE DOG (II):
MYELOID METAPLASIA, HISTIOCYTOSIS AND HYPERSPLENISM
Key facts
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Poorly described, idiopathic condition causing
diffuse splenomegaly in the dog |
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Haematology and clinical chemistry not diagnostic |
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Unique set of histological changes in the
spleen |
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Histopathology essential: giant cells in splenic
parenchyma predict fatal outcome |
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30% of dogs will survive 12 months |
Aim of communication
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To summarise CURRENT KNOWLEDGE on this condition
including prognostic data |
Haematology and serum chemistry
Not specific! May include:
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Normochromic, normocytic anaemia (30% of cases) |
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Leukocytosis (35% of cases) |
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Total and direct bilirubin values elevated
in 30% and 60% of cases, respectively |
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Clinical diagnosis of autoimmune haemolytic
anaemia in 20% of dogs |
Macroscopical pathology
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Uniform large, pale red spleen |
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Embedded, contiguous but indistinct nodules
in 61% of cases |
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Bulging, coarsely granular cut surface that
fails to exude blood |
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Increased consistency or increased fragility |
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Thrombosis and/or foci of infarction in 69%
of cases |
Histological pathology
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Unique features: combination of myeloid hyperplasia
(extramedullary haematopoiesis), excessive erythrophagocytosis, and histiocytosis
(may become histiocytic neoplasia with spread to other organs) |
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Thrombosis and infarction |
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Multiorgan involvement with histiocytic neoplasia
at time of necropsy in 53% of cases |
Aetiology
Speculative, may be subsequent to protozoon
infections (Babesia, Ehrlichia); systemic infections; immune-mediated
(AIHA)
Prognosis
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Presence of giant cells in splenic parenchyma
the only reliable prognostic feature, indicative of an extremely
poor prognosis with a fatal outcome within 0-16 months (median time to
death, 1 month) |
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Only 30% of dogs survived > 12 months! None
of these cases had giant cells at time of splenectomy |
MEANINGFUL PROGNOSIS DEPENDS ON A DETAILED MACRO
AND HISTOLOGICAL EXAMINATION OF THE SPLEEN FOLLOWING SPLENECTOMY
Reference
Spangler WT et al Splenic Myeloid
Metaplasia, Histiocytosis, and Hypersplenism in the Dog (65 cases). Veterinary
Pathology 36:583-593 (1999)
For further information contact
VetPath Veterinary Pathologists
P.O. Box 8464
Pretoria 0001
Tel: (012) 529 8345/6
e-mail: info@vetpath.co.za 
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