Functional and morphological studies on blood platelets in a thrombasthenic horse.

The study investigates a case of a horse showing symptoms of clotting disorders, diagnosed with a condition similar to a rare human platelet disorder named Glanzmann’s Thrombasthenia.

Case Presentation

• The subject of study was a four-year-old Standardbred gelding or male horse. The horse had a history of an intermittent nose bleed and spontaneous occurrence of tiny spots and larger patches of bleeding into the skin of the nose and mouth. These symptoms had been prevalent for about three and a half years.
• The horse underwent a routine blood test and biochemical analysis. However, no remarkable signs pointing towards a disease or disorder were detected.

Suspected Condition and Further Testing

• Despite normal findings from initial tests, a platelet disorder, thrombocytopathy, was suspected. This conclusion was based on the observation that some important parameters involved in blood clotting – activated partial thromboplastin time, one stage prothrombin time, plasma fibrinogen, and platelet count – were all normal.
• To confirm the suspicion, the horse’s blood platelets were subjected to multiple tests. They failed to clump together or aggregate in the presence of several substances that usually trigger this action – serotonin, adenosine diphosphate, collagen at a typical concentration, and endoperoxide analogue U46619.
• However, a significantly high concentration of collagen did manage to induce platelet aggregation. A diminished response was observed to the calcium ionophore A23187, and while platelets degranulated (released their contents), the resulting aggregates were unstable.

Diagnosis and Comparison to Human Disorder

• The production of thromboxane, a substance that promotes platelet aggregation, was inferred to be reduced. This was deduced by measuring the concentration of its stable by-product, thromboxane B2, upon exposure to collagen and ADP.
• Based on all findings, the horse was diagnosed with a disorder similar to thrombasthenia – a condition that affects platelets’ ability to aggregate and form a blood clot. This syndrome was comparable to a variant of Glanzmann’s Thrombasthenia (Type II) encountered in humans.