Purpura (Fig. 11.15), petechiae and ecchymoses may be caused by a coagulation or platelet disorder, or by an abnormality of the vessel wall or the surrounding dermis. Some common causes are listed in Table 11.8. In general, coagulation defects give rise to ecchymoses and external bleeding. Platelet defects present more often as purpura, although bleeding and ecchymoses can still occur. Vasculitis of small vessels causes pur-pura, often palpable and painful, but not bleeding; this is discussed earily. Purpura from vasodi-latation and gravity is seen in many diseases of the legs, especially in the elderly (defective dermis around the blood vessels), and seldom requires extensive investigation.
Cryoglobulinaemia is a rare cause of purpura, which is most prominent on exposed parts. It may also cause cold urticaria and livedo reticularis.
The condition may be idiopathic, or secondary to myeloma, leukaemia, a previous hepatitis C infection or an autoimmune disease.
The most common cause of purpura is trauma, espe-cially to the thin sun-damaged skin of elderly forearms. When purpura has no obvious cause, investigations should include a platelet count, prothrombin time, activated partial thromboplastin time (APTT), a full blood count and biochemical screen. Electrophoresis is needed to exclude hypergammaglobulinaemia and paraproteinaemia. Cryoglobulinaemia should also be excluded. To help detect a consumptive coagulopathy, a coagulation screen, including measurement of fibrino-gen and fibrin degradation products, may be necessary. The bleeding time, and a Hess tourniquet test for cap-illary fragility, help less often. Skin biopsy will confirm a small vessel vasculitis, if the purpura is palpable.
Treat the underlying condition. Replacement of re-levant blood constituents may be needed initially. Systemic steroids are usually effective in vasculitis .