Purpura may occur with bacterial, fungal, viral, or rickettsial infections, or with parasitic infestations, including protozoan, often as a consequence of a complex, multifactorial process. Special forms include:
— Bacterial sepsis due to various organisms can cause petechiae or purpura, macules or papules, hemorrhagic bullae, erosions, ulcers, or widespread ecchymoses and cutaneous infarctions (purpura fulminans, see below).
— Ecthyma gangrenosum may accompany infections with Pseudomonas sp., Klebsiella sp., Aeromona hydrophilia, or Escherichia coli in patients with severe granulocytopenia or immune compromise. Lesions begin as erythematous or purpuric macules and progress to hemorrhagic or necrotic vesicles or bullae, then to edematous, hemorrhagic plaques, and finally to indurated painless ulcers.
— Meningococcemia may cause erythematous papules that progress to widespread petechiae, purpura, and ecchymoses. Acrocyanosis and peripheral gangrene may occur.
— Scarlet fever is characterized by a diffuse, erythematous rash often with confluent petechiae in skin folds (Pastia lines). Streptococcal pharyngitis without scarlet fever may also be associated with petechiae.
— Rickettsial infections cause cutaneous lesions, beginning as urticarial macules and progressing to petechiae, ecchymoses, hemorrhagic bullae, and extensive skin necrosis.
— In Lyme disease, the characteristic cutaneous lesion is erythema migrans, an annular, expanding plaque that may contain a purpuric macule or papule, or a hemorrhagic bulla.