An outbreak of compressive myelopathy due to pyogranulomatous reaction to the oily adjuvant of the foot-and-mouth disease vaccine - case report

ABSTRACT Cases of compressive myelopathy syndrome associated with post vaccinal pyogranulomas were diagnosed post mortem in three cows from a farm in Minas Gerais state, Brazil. These cows presented ataxia and bilateral paresis of the pelvic limbs, which evolved to paralysis, and sternal recumbence. On necropsy, locally extensive areas of the longissimus dorsi muscle were replaced by pyogranulomas supported by moderate amounts of fibrous connective tissue. On the cut surface, some nodules contained yellowish and viscous fluid (purulent exudate) or whitish fluid (interpreted as the oily adjuvant of a vaccine). In the spinal canal of the subjacent vertebrae, compressing the spinal cord, were pyogranulomas identical to those described in the skeletal muscle. Histologically, the pyogranulomas were composed of a central clear vacuole (consistent with the space left by the oil adjuvant droplets), surrounded by neutrophils and, more externally, by large numbers of epithelioid macrophages and fewer multinucleated giant cells. In the white matter of the spinal cord were numerous well-defined, clear vacuoles (Wallerian degeneration). The association of the clinical history and pathological findings allowed the diagnosis of compressive myelopathy associated with pyogranulomatous reaction to the oily adjuvant of the foot-and-mouth disease vaccine, in this case, due to its inadequate application.