Atypical granulation in neutrophils of a domestic shorthair cat

A 13-year-old male domestic short-hair cat presented for evaluation of labored breathing, hyporexia, and lethargy. Pertinent initial diagnostics yielded leukocytosis, characterized by neutrophilia and monocytosis. Numerous small, round, magenta granules were observed within all neutrophils in Wright-Giemsa-stained blood films on the day of presentation and the day thereafter. No other neutrophil morphologic abnormalities were present, making cytoplasmic toxicity highly unlikely. Hyperadrenocorticism was diagnosed based on the lack of suppression in a low-dose dexamethasone suppression test, and without other diagnostics, the cat was discharged on trilostane therapy. Neutrophil granules did not stain with Alcian blue pH 1.0, periodic acid-Schiff (PAS), PAS and Alcian blue pH 2.5, and toluidine blue. Electron microscopy identified no differences in the morphology of the secretory granules or other neutrophil features. Metabolic screening tests of the cat's urine did not identify a genetic metabolic disorder. However, serum α- and β -hexosaminidase (HexA and HexB) activities were 4.3% and 0% of normal controls, respectively, which is supportive of GM2-gangliosidosis, that is, Sandhoff disorder. However, the historical, clinical, and electron microscopy findings did not provide evidence to confirm this genetic defect. To the author's knowledge, this is the first case of magenta-staining granules within neutrophils in a breed other than a Birman, Siamese, or Himalayan.