RADIOGRAPHIC AND PATHOLOGIC FEATURES OF OSTEOPETROSIS IN TWO PERUVIAN PASO FOALS

The radiographic and pathologic findings of two Peruvian Paso foals with osteopetrosis are described. Both foals, one male and one female, presented with respiratory difficulty, brachygnathia and failure to rise after birth. Both foals were mildly anemic, hypogammaglobulinemic and had elevations in serum alkaline phosphatase. Increased medullary bone opacity was noted on radiographs of the extremities, spine and skull 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 the osteopetrotic bones. One foal developed a bacterial pneumonia. Both foals were euthanized due to failure to thrive. Histopathology and electron microscopy documented these foals to have normal osteoclastic numbers 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, lethal autosomal recessive form of osteopetrosis described in humans. Osteopetrosis has not been previously described in a female foal.