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Purpura

BACKGROUND

Purpura, or bleeding into the skin, may be an innocent finding in minor trauma or the first sign of a life-threatening disease. Pinpoint areas of hemorrhage are called petechiae; large, confluent patches are referred to as ecchymoses. Purpura may result from extravascular, intravascular, or vascular processes. Nonpalpable purpuric lesions develop from extravascular and intravascular phenomena, whereas those that are palpable result from a vascular process. Conditions associated with each type are listed in Table 58-1.

TABLE 58-1Pathophysiology of Purpura

PATHOPHYSIOLOGY

Extravascular Purpura

Trauma is the most common cause of extravascular purpura in children. Nonblanching, nonpalpable purple patches following accidental trauma vary from a few millimeters to many centimeters in diameter and are usually located over bony prominences such as the knees, elbows, extensor surfaces of the lower legs, forehead, nose, and chin. In otherwise healthy children, petechiae occur occasionally on the face and chest after vigorous coughing or vomiting and in dependent areas after standing in place or engaging in vigorous physical activity for long periods.

The presence of purpura on protected or unexposed sites, such as the buttocks, spine, genitalia, upper thighs, and upper inner arms, suggests the possibility of nonaccidental trauma (Figure 58-1). In some cases, the shape of the bruise provides a clue as to the object used to inflict the injury (see Chapter 39).1

FIGURE 58-1.

Belt-buckle imprint from a beating (arrow).

Scars, nutritional deficiencies (e.g. vitamin C, protein), hereditary defects in collagen synthesis (e.g. Ehlers-Danlos syndrome), and other factors that increase skin fragility and decrease the tensile strength of the tissue surrounding vessels in the dermis and fat increase the risk of extravascular purpura after trauma.

Intravascular Purpura

Intravascular purpura results from disorders that interfere with normal coagulation. Nonpalpable petechiae and large ecchymoses may be present, and mucosal bleeding may be evident; in severe cases, bleeding may occur in the joints, deep soft tissues, kidneys, gastrointestinal tract, central nervous system, and other viscera. Disorders associated with intravascular purpura may result from abnormalities in platelet number or function, or from deficiencies in coagulation factors. These disorders include autoimmune thrombocytopenic ...

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