The title "purpura hemorrhagica" is chosen purposely to withdraw attention from the term "essential thrombocytopenia." Several observers have reported cases of this disease in which the platelets were relatively high or normal in number and yet hemorrhagic phenomena were present. On the other hand, platelets may number less than 100,000 without hemorrhagic phenomena. We have confirmed these observations in our group of cases and are convinced that the platelet factor, although of importance, is not an essential feature in this disease.
Capillary hyperpermeability, or capillary weakness, is essential for the production of hemorrhagic phenomena, which may occur if this condition is present alone or if both capillary hyperpermeability and platelet deficiency are found. However, if platelet deficiency is present alone, the hemorrhagic phenomena may not result. We feel, therefore, that the most important single factor, or in other words the common denominator, in this disease is capillary hyperpermeability.