RADIOGRAPHIC AND PATHOLOGICAL FEATURES OF OSTEOPETROSIS IN 2 PERUVIANPASO FOALS

The radiographic and pathologic findings of two Peruvian Paso foals wi th osteopetrosis are described. Both foals, one male and one female, p resented with respiratory difficulty, brachygnathia and failure to ris e after birth. Both foals were mildly anemic, hypogammaglobulinemic an d had elevations in serum alkaline phosphatase. Increased medullary bo ne opacity was noted on radiographs of the extremities, spine and skul l in both foals. A lack of normal cortical:medullary bone distinction was evident radiographically. The medullary primary spongiosa appeared to run in parallel columns away from the physes of all long bones and the vertebrae. This created a distinctive hour glass appearance to th e osteopetrotic bones. One foal developed a bacterial pneumonia. Both foals were euthanized due to failure to thrive. Histopathology and ele ctron microscopy documented these foals to have normal osteoclastic nu mbers but lack normal ruffled borders, lack of a clear zone and normal lysosomal numbers indicative of cellular dysfunction. These clinical, radiographic and pathologic findings are similar to the juvenile, let hal autosomal recessive form of osteopetrosis described in humans. Ost eopetrosis has not been previously described in a female foal.