Homozygous
protein C deficiency or homozygous
protein S deficiency are rare
genetic diseases with catastrophic and fatal
purpura fulminans-like or thrombotic complications occurring during the neonatal period. These diseases can now be successfully treated.
Purpura fulminans is at least in part a cutaneous manifestation of the syndrome of systemic
DIC. It is characterized by microvascular
thrombosis in the dermis followed by perivascular
hemorrhage,
necrosis, and minimal
inflammation. Laboratory findings are consistent with
DIC. Although the pathogenesis is not fully understood, the
DIC in
purpura fulminans appears to involve the skin selectively. The development of
purpura fulminans from homozygous
protein C or
protein S deficiencies can be separated into the two distinct phases. The first phase is the time period when the initial reversible lesions develop and grow. This reversible progression can be halted and reversed with the administration of
protein C or
protein S. The second phase is the irreversible stage in which the lesion continues to develop into a necrotic lesion, whether or not treated with
protein C. This irreversible lesion will ultimately develop into a large full-thickness necrotic injury of the skin. It is very similar to the lesions seen in idiopathic
purpura fulminans,
warfarin-induced skin
necrosis, and acute infectious
purpura fulminans. Unfortunately, our current understanding of the mechanism or mechanisms of the induction and propagation of the
purpura fulminans-like lesions in homozygous
protein C or
protein S deficiencies is minimal, since it has never been studied. We can only speculate on the mechanism based on laboratory data and comparison with the little that is known about the other similar types of lesions.