Delta-Storage Pool Disease: An Underestimated Cause Of Unexplained Bleeding

Platelet dense granules are small organelles that contain high concentrations of adenine nucleotides, serotonin, calcium and phosphates. During platelet activation, their contents are released into the extracellular environment. dstorage pool disease (d-SPD) is a platelet function disorder characterized by a reduced number of dense bodies and/or a deficiency of their intragranular content. The causes of d-SPD are variable and can be classified into (1) congenital diseases including Hermansky-Pudlak and Chediak-Higashi syndromes, (2) nonsyndromic inherited platelet disorders, and (3) acquired forms, most often associated with hematologic malignancies (myeloproliferative syndrome, acute leukemia, or myelodysplastic syndromes). Patients generally demonstrate mild to moderate bleeding diathesis. However, bleedings can on occasion be severe or life-threatening, in particular when patients require invasive procedures. Thus, rapid and accurate diagnosis is crucial to initiate appropriate therapy that in turn prevents bleeding. This platelet disorder is considered to be relatively frequent, but it is often underdiagnosed as the biological diagnosis is highly complex. Typically, d-SPD is associated with a lack of second wave of platelet aggregation in response to low agonist concentrations. Nevertheless, patients affected with d-SPD may also have a normal pattern of platelet aggregation response. Therefore, the definitive diagnosis must be confirmed by specialized tests to demonstrate the absence or marked reduction of dense bodies. In this purpose, it would appear advisable to perform electron microscopy associated to nucleotides and serotonin quantification. In conclusion, d-SPD represents a complex disorder possessing diverse clinical and biological aspects whose accurate diagnosis requires an extremely high level of expertise.