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Purpuric Maculopapular Skin Lesions

  1. Purpura represents extravasation of red blood cells outside the cutaneous vessels and, unlike erythema, cannot be blanched. Purpura can be classified as non-palpable (macular) and palpable (papular).
  2. Non-palpable purpura results from bleeding into the skin without associated inflammation of the vessels and indicates either a bleeding diathesis or fragile blood vessels. Non-palpable purpura can be petechial (macules < 3 mm) or ecchymotic (macules > 3 mm).
  3. Thrombocytopenia causes petechiae, whereas abnormalities in the clotting cascade commonly cause ecchymoses.
  4. Necrotic ecchymoses are found when thrombi form in dermal vessels and lead to infarction and hemorrhage, e.g., disseminated intravascular coagulation (DIC).
Palpable purpura results from inflammatory damage to cutaneous blood vessels, as in vasculitis.

Causes of Purpura

I. Primary cutaneous disorders

A. Nonpalpable

1. Trauma

2. Solar purpura

3. Steroid purpura

4. Capillaritis

5. Livedoid vasculitisa

II. Systemic diseases

A. Nonpalpable

1. Clotting disturbances

a. Thrombocytopenia (including ITP)

b. Abnormal platelet function

c. Clotting factor defects

2. Vascular fragility

a. Amyloidosis

b. Ehlers-Danlos syndrome
c. Scurvy

3. Thrombi

a. Disseminated intravascular coagulation

b. Monoclonal cryoglobulinemia

c. Thrombotic thrombocytopenic purpura

d. Warfarin reaction

4. Emboli

a. Cholesterol

b. Fat

5. Possible immune complex

a. Gardner-Diamond syndrome (autoerythrocyte sensitization)

b. Waldenstrom's hypergammaglobulinemic purpura

B. Palpable

1. Vasculitis

a. Leukocytoclastic vasculitis

b. Polyarteritis nodosa

2. Emboli

a. Acute meningococcemia                         

b. Disseminated gonococcal infection      

c. Rocky Mountain spotted fever
d. Ecthyma gangrenosum

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