Chapter 29-13: Purpura/Petechiae

TEXTBOOK PRESENTATION

Purpura and petechiae are seen in patients with bleeding diatheses or vascular damage. Petechiae are capillary hemorrhages that present as nonblanching, pinpoint, red spots over dependent body parts, most commonly the lower extremities. They are often associated with severe thrombocytopenia. Purpura are larger hemorrhages into the skin. Purpura are associated with a variety of life-threatening diseases, such as vasculitis and sepsis.

DISEASE HIGHLIGHTS

1. Description of the lesion: petechiae are red, blue or purple, nonblanching, pinpoint spots. Purpura are larger (up to several centimeters) nonblanching macules, papules, or plaques that may or may not be palpable (Figure 29-15).

2. Both purpura and petechiae are, to some degree, nonblanching (ie, the color cannot be compressed out of the lesion by pressure).

3. The shape of these lesions is variable, ranging from stellate to round or oval or targetoid to retiform (netlike).

4. The color, texture, and configuration of these lesions will be helpful in constructing a differential diagnosis of the cause.

5. The differential diagnosis of purpura/petechiae is vast, and many classification schemes have been proposed. The first step is to differentiate ecchymoses from purpura and petechiae.

6. Ecchymoses

   1. Ecchymoses are the most common form of hemorrhage in the skin.

   2. They are typically induced by trauma and, therefore, are seen on trauma-prone sites, such as the dorsal hand, forearm, lateral thigh, and shin.

   3. The shape of ecchymoses tends to be geometric (rectangular) or linear because they are induced by an external force.

   4. Predisposing factors to ecchymoses include weakening of the dermal structure secondary to age, corticosteroid use, solar damage, and vitamin C deficiency (scurvy) as well as coagulation defects.

7. Petechiae are most commonly associated with thrombocytopenia.

8. Purpura

   1. Like petechiae, purpura signify hemorrhage into the skin.

   2. The hemorrhage may

      1. Be simple extravasation through leaky vessel walls.

      2. Be accompanied by inflammation that is damaging vessel walls. (These lesions are often partially blanching because the inflammatory component blanches while the hemorrhagic component does not.)

      3. Be the result of occlusion of a vessel leading to ischemic damage to the skin.

   3. The degree to which purpuric lesions are palpable is helpful diagnostically.

      1. Nonpalpable hemorrhage in the skin is most concerning for thrombocytopenia or abnormal platelet function.

      2. Extravasation of blood alone into deep tissue layers can produce a nodule (such as occurs with a hematoma).

      3. Edema associated with the vessel injury (such as in cases of inflammatory vasculitis) may cause a palpable lesion.

         1. Palpable purpura can be a sign of serious, potentially life-threatening, illness (eg, Rocky Mountain spotted fever, acute meningococcemia, disseminated gonococcal infection).

         2. Evaluation should include tests for vasculitis and, in the right setting, infectious causes (possibly including empiric treatment).

EVIDENCE-BASED DIAGNOSIS

1. An evaluation of clotting (platelet number, function, and measures of coagulation) is indicated to determine whether purpura and petechiae are symptoms of a coagulopathy, thrombocytopenia, or ...