Granulomatous leptomeningitis in beagle dogs

A granulomatous leptomeningitis was seen in seven laboratory Beagle dogs (four males, three females), 14 to 15 months old, that had been used as control or experimental subjects in a toxicologic study. The dogs were clinically normal during the experimental period. Microscopic lesions were characterized by typical noncaseating granulomas in leptomeninges and slight scattered perivascular cuffing in gray and white matter throughout the central nervous system, with no site of predilection. Although no microorganisms could be found by ordinary light microscopic examination, there was a positive reaction for Escherichia coli antigen in the cytoplasm of macrophages, which corresponded to periodic acid-Schiff-positive, calcium-negative, and iron-negative materials in the granulomas and cuffs. Electron microscopic examination revealed that these materials were large phagolysosomes indicative of abnormal lysosomal function. These findings indicate that at least some cases of canine granulomatous leptomeningitis could be very likely caused by E. coli and represent an entity distinct from classical canine granulomatous meningoencephalitis.