JPC SYSTEMIC PATHOLOGY
SIGNALMENT (JPC #1811021): Adult male dog
HISTORY: Blood smear from an adult male dog obtained for use by an investigator performing research in leukocyte chemotaxis. Screening test failed to give acceptable baseline results. White cell count - 14,300/ml. Hemogram from Coulter Model S+11 reported 88% lymphocytes, based on distribution of cell size.
HISTOPATHOLOGIC DESCRIPTION: Blood smear: The white and red cell counts appear adequate on this good quality smear. The differential count is: segmented neutrophils - 858 (6%), band neutrophils - 7150 (50%), monocytes - 3432 (24%), lymphocytes - 1859 (13%), and eosinophils - 1001 (7%). The predominant leukocyte type is the neutrophilic band cell. Over 90% of the granulocytes (neutrophils and eosinophils) have slightly indented round, band-shaped, or bilobed nuclei with smooth nuclear membranes and coarsely clumped (mature) chromatin. There are occasional polychromatophilic erythrocytes and platelet numbers are adequate.
MORPHOLOGIC DIAGNOSIS: Blood smear: Granulocytic hyposegmentation, diffuse, with mature chromatin pattern, breed unspecified, canine.
CONDITION: Pelger-Huët anomaly
- Pelger-Huët anomaly is an uncommon, usually benign, autosomal dominant hereditary condition due to mutations in the lamin B receptor gene and characterized by hyposegmentation of granulocytes with a coarse, mature chromatin pattern despite their immature shape; alterations are especially noticeable in the neutrophil series
- Documentation of nuclear hypolobulation of both monocytes and megakaryocytes suggests a stem cell defect in the nuclear segmentation process
- It has been described in dogs (Australian shepherd (most common); Australian cattle dog; Basenji; Border collie; Boston terrier; cocker spaniel; black and tan, blue tick, and red bone coonhounds; German shepherd dog; English and American foxhounds; Samoyed; and mongrels), cats (domestic shorthair), rabbits, a horse, and humans
- Heterozygous phenotype: Does not affect the animal’s health, and neutrophils respond normally to function tests (leukocyte adherence, chemotaxis, phagocytosis, and bactericidal action); most commonly encountered form
- Homozygous phenotype: This is rare and usually lethal in utero; it has been described in rabbits, and one stillborn kitten; the kitten and most of the rabbits had concurrent chondrodysplasias
TYPICAL CLINICAL FINDINGS: None
TYPICAL GROSS FINDINGS:
- Usually none
- With the homozygous form, fetal death and/or skeletal abnormalities due to chondrodysplasias are seen concurrently
TYPICAL LIGHT MICROSCOPIC FINDINGS:
- Heterozygous phenotype: There is a normal total leukocyte count and persistent left shift with a preponderance of band neutrophils (30-70% of total) and younger forms; the affected cells have a coarse and mature chromatin pattern and may be bilobate (“spectacle” or “pince-nez”); eosinophil and basophil morphology may also be affected; it is difficult to distinguish from an inflammatory leukogram and may be found concurrently in affected animals with severe bacterial infections
- Homozygous phenotype: Granulocytes have round to oval nuclei with a very coarse or “chunky” chromatin pattern; exposure of heterozygous Pelger-Huët rabbits to colchicine has transiently produced homozygous type nuclear changes
ADDITIONAL DIAGNOSTIC TESTS:
- Definitive diagnosis requires demonstration of granulocytic nuclear changes in blood smears of parents, siblings, or other relatives
Other conditions that result in hyposegmented leukocytes in animals:
- Left shift: Band neutrophils and younger forms have nuclei with less aggregated chromatin, there often are cytoplasmic toxic changes (vacuolation, basophilia, Döhle bodies, or toxic granulation), and the condition is not persistent with treatment
- Pseudo-Pelger-Huët anomaly (acquired Pelger-Huët anomaly): This is an acquired nuclear hyposegmentation of neutrophils and/or eosinophils with coarse, mature chromatin pattern; pseudo-Pelger-Huët Anomaly is transient and may resolve if the underlying condition is diagnosed and treated properly; most often reported in cattle with ruminal atony but also seen in cats with feline leukemia and preleukemia, a dog following treatment with multiple drugs (including TMS), a horse with disseminated granulomatous disease of unknown origin, and Wistar rats with myeloid leukemia
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