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CHAPTER 25: THE DIFFERENTIAL DIAGNOSIS OF PURPURA

CASE 25-1

A 40-year-old man with a recent history of cellulitis is admitted to the hospital with fever, chills, and a progressive rash most prominent on the extremities. Central necrosis and eschar formation develop in some of the larger lesions. Blood cultures grow methicillin-resistant Staphylococcus aureus. Complete blood count shows leukocytosis, anemia, and thrombocytopenia.

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What is the one most likely diagnosis?

(A) Amyloidosis

(B) Pigmented purpuric dermatoses

(C) Vitamin C deficiency

(D) Purpura fulminans

(E) Leukocytoclastic vasculitis

The correct answer is (D), purpura fulminans.

Purpura fulminans is the cutaneous manifestation of microvascular occlusion and represents a medical emergency. It results in a branching or retiform pattern of purpura, with rapid progression to necrosis that begins centrally. There are many causes of purpura fulminans, including postinfectious purpura fulminans which is most commonly secondary to varicella, Streptococci, Neisseria meningitidis, Staphylococcus aureus. Sepsis-related purpura fulminans presents as described above in the clinical case. It is important to treat the underlying infection, assess for disseminated intravascular coagulation, check levels of protein C and S, and treat as appropriate.

Pigmented purpuric dermatoses are asymptomatic macules typically on the lower legs. Vitamin C deficiency presents with perifollicular hemorrhage, while leukocytoclastic vasculitis is characterized by palpable purpura which is generally not retiform in nature, even when it may present as hemorrhagic bullae.

CASE 25-2

A 62-year-old man presents with a 3-month history of asymptomatic, nonpalpable, nonblanching, cayenne pepper patches on the legs. He has no systemic complaints, denies any new medications, or trauma.

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What is the one most likely diagnosis?

(A) Schamberg's purpura

(B) Vitamin C deficiency

(C) Stasis dermatitis

(D) Leukocytoclastic vasculitis

(E) Cholesterol emboli

The correct answer is (A), Schamberg's purpura.

Schamberg's purpura is characterized by asymptomatic or slightly pruritic, orange or brown macules (nonpalpable) typically on the lower extremities. The eruption is generally chronic and may persist for years. It is not a manifestation of systemic disease, and generally resolves spontaneously.

Vitamin C deficiency presents with perifollicular hemorrhage. Leukocytoclastic vasculitis is characterized by palpable purpura. Cholesterol emboli typically manifest with distal livedo reticularis, and stasis dermatitis typically has more diffuse dyspigmentation and is accompanied by lower extremity edema.

CASE 25-3

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