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.

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

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 purpura, acute leukemia with thrombocytopenia, aplastic anemia, sepsis with disseminated intravascular coagulation (DIC), and various coagulation factor deficiencies.

Primary immune thrombocytopenic purpura (ITP) is the most common type of intravascular purpura in previously healthy children. This condition was previously termed idiopathic thrombocytopenic purpura. Patients typically present acutely 2 to 4 weeks after a viral illness with petechiae and ecchymoses after minimal or no apparent trauma (Figure 58-2). The incidence peaks in the later winter and early spring. Occult blood can often be detected in the stool and urine, but clinically significant hemorrhage is unusual. ITP is associated with the development of immunoglobulin (Ig) G antibodies that bind to platelets and trigger increased destruction by the reticuloendothelial system. Platelet counts may dip below 10,000/mm³ for several weeks but usually return to normal within 4 to 6 weeks. Other cell lines are unaffected, and patients appear well without fever or other systemic symptoms. Antiplatelet antibodies and thrombocytopenia can also develop in other less common disorders, including systemic lupus erythematosus, leukemia, lymphoma, and drug reactions.

Purpura can be an early manifestation of leukemia or aplastic anemia. These disorders may also be associated with anorexia, weight loss, fatigue, joint pain, and a persistent flulike illness. Hepatosplenomegaly, lymphadenopathy, and bone tenderness may be prominent. Bone marrow dysfunction from both leukemia and aplastic anemia may affect all cell lines, and patients may present with serious cutaneous infections or sepsis.

Purpura fulminans presents with rapidly progressive ecchymoses that may cover large areas of skin (Figure 58-3). It represents the cutaneous manifestation of sepsis and DIC. Hemorrhage into multiple organs may also occur in this life-threatening process. Purpura is usually associated with ischemia, and in patients who survive, large areas of necrosis can develop. In normal children, meningococcal and Rocky Mountain spotted fever infections are probably the most common cause of purpura fulminans followed by Streptococcus, Haemophilus, and Staphylococcus sepsis, particularly in asplenic patients. A number of other bacterial, viral, and fungal organisms have been implicated in immunocompromised patients.^2,3 Finally, DIC may result from acquired or occult heritable protein C or protein S deficiency after benign childhood infections such as varicella.