Platelet Storage Pool Disease
Storage Pool Disease (SPD) is the name given to several rare disorders in which the platelet granules are affected. Granules are storage spaces inside each platelet. During the process of making a platelet plug, the platelets change shape. Chemicals inside the granules are pushed out into the bloodstream. This is called secretion. These chemicals from the granules signal other platelets to come and help. The chemicals allow the next step in forming a platelet plug, aggregation, to happen.
With a Storage Pool Disease (SPD), there may not be enough of a certain type of granule, the granule may be abnormal, or there may not be enough of the chemicals it is supposed to hold. In Delta Storage Pool Disease, the delta granules (also called dense granules) are affected. In Alpha Storage Pool Disease, it is the alpha granules. Alpha SPD is also called Gray Platelet Syndrome. This is because the platelets of someone with Alpha SPD look gray when viewed under a microscope. It is possible to have Alpha/Delta SPD in which both types of granules are affected.
When platelets are not able to store chemicals or secrete them when needed, they can’t let other platelets know to come and help form a plug. It takes longer for a clot to form. SPD usually results in mild to moderate bleeding symptoms. Bleeding lasts longer than normal but the body is usually able to make it stop. People with SPD rarely require treatment except when they are having surgery or have a serious injury.
Testing for Storage Pool Disease
The platelet count may be below normal.
Looking at the platelets under an electron microscope can show that there are few or no dense granules. With Alpha SPD, the platelets look large and gray.
The bleeding time test is sometimes longer than normal.
Platelet aggregation tests are abnormal. The platelets aggregate normally in response to some of the test chemicals (agonists) and not to others.
Treatment for Storage Pool Disease
People with SPD may respond to DDAVP® . Transfusion with donated platelets may be needed for severe bleeding.