Purpura and Disorders of Microvascular Occlusion

Published on 05/03/2015 by admin

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Purpura and Disorders of Microvascular Occlusion

Purpura represents visible hemorrhage into the skin or mucous membranes; as a result and in contrast to erythema due to vasodilation, it is nonblanching upon application of external pressure.

Purpura can be primary, where hemorrhage is an integral part of lesion formation, or secondary, where there is hemorrhage into established lesions due to factors such as venous hypertension, gravity, or thrombocytopenia.

As purpuric lesions fade, their color evolves from red-purple or blue to brown or yellow-green.

Primary purpura has a broad differential diagnosis, and it is helpful to categorize purpuric lesions based on their size and morphology.

Petechiae: ≤3 mm and macular (Table 18.1; Fig. 18.1A).

Ecchymoses: usually >1 cm and macular with round/oval to slightly irregular borders, and typically have an element of trauma in their pathogenesis (see Table 18.1; Fig. 18.1B); a greater volume of hemorrhage leads to a hematoma, which is palpable.

Retiform purpura: reticulated, branching or stellate morphology, which reflects occlusion of the vessels that produce the livedo reticularis pattern (see Chapter 87; Tables 18.2 and 18.3; Figs. 18.1C and 18.218.9).

Classic ‘palpable purpura’: round red-purple papules that are occasionally targetoid, with a component of blanching erythema in early lesions; represents the most common presentation of cutaneous small vessel vasculitis (see Chapter 19; Fig. 18.1D).

A biopsy specimen can be helpful in determining the etiology of a purpuric eruption, e.g. whether there is vascular occlusion with minimal inflammation or vasculitis (inflammation and fibrinoid necrosis of vessel walls); because secondary changes of vasculitis may be seen when an older lesion of microvascular occlusion is sampled, and likewise a late lesion of vasculitis may have minimal residual inflammation, it is preferable to choose a well-developed but relatively early lesion (e.g. 24–48 hours old).

Selected Microvascular Occlusion Syndromes (See Table 18.2)

Other Purpuric Disorders

Pigmented Purpuric Dermatoses (Capillaritis)

Group of disorders characterized by clustered petechial hemorrhage due to inflammation affecting capillaries.

Schamberg’s disease: most common form, occurring in both children and adults; recurrent crops of discrete yellow-brown patches containing pinpoint petechiae (‘cayenne pepper’) on the lower legs > thighs, buttocks, trunk, and arms (Fig. 18.10A); the yellow-brown color reflects deposits of hemosiderin, derived from extravasated RBCs, within the dermis.

Purpura annularis telangiectodes (of Majocchi): favors adolescent girls and young women; expanding annular plaques with punctate telangiectasias and petechiae in their borders (Fig. 18.11).

Lichen aureus: solitary golden to rust-colored or purple-brown patch or thin plaque, typically on the leg overlying a perforator vein.

Other forms include pigmented purpuric lichenoid dermatitis presenting as red-brown papules and eczematid-like purpura with scaling and pruritus; these variants favor the lower legs of men.

DDx: ‘stasis purpura’ presenting as petechiae superimposed on diffuse hemosiderin deposition on the legs (see Fig. 18.10B); purpuric forms of allergic contact dermatitis, drug eruptions or mycosis fungoides; suction-induced purpura (e.g. with cupping), hypergammaglobulinemic purpura of Waldenström, angioma serpiginosum; for lichenoid variant: primarily small vessel vasculitis.

Rx: difficult; topical CS if pruritic, phototherapy.