Version June 2024
| Population commonly affected | Common clinical features | Pertinent histopathologic findings | |
| Peripheral scale | |||
| Tinea corporis | Children and adults | Annular erythematous plaques with peripheral leading scale | Hyphae in the stratum corneum; KOH preparation is preferred initial test |
| Pityriasis rosea | Children and young adults | Thin erythematous plaques on trunk and proximal extremities in "Christmas tree" pattern; may have large initial lesion (herald patch) | Focal parakeratosis, epidermal spongiosis, perivascular lymphohistiocytic infiltrate, RBC extravasation |
| Superficial erythema annulare centrifugum | Children and adults | Erythematous plaques with trailing scale on face, trunk, or extremities | Parakeratosis, spongiosis, superficial intense perivascular lymphohistiocytic infiltrate |
| Porokeratosis | Children and adults | Plaque with very thin rim of scale at periphery; multiple clinical variants exist | Cornoid lamella - thin column of parakeratosis |
| Vesicles | |||
| Linear IgA bullous dermatosis | Children and adults | Annular clusters of tense bullae on an inflammatory base | Subepidermal bullae with neutrophilic infiltrates; direct immunofluorescence reveals linear deposits of IgA at the DEJ |
| Pustules | |||
| Subcorneal pustular dermatosis | Most common in adults over 40 | Intertriginous and flexural flaccid pustules and crusted plaques | Subcorneal pustules with neutrophils |
| Purpura | |||
| Purpura annularis telangiectodes of Majocchi | Most common in young women and female adolescents | Round patches on the lower extremities that do not blanch with pressure | Perivascular lymphocytic infiltrates and extravasated erythrocytes |
| Acute hemorrhagic edema of infancy | Children under the age of two | Urticarial plaques progressing to purpuric plaques | Leukocytoclastic vasculitis |
| Henoch-Schönlein purpura | Children and adults | Palpable purpura on the lower extremities; arthritis, abdominal pain, and hematuria may be present | Leukocytoclastic vasculitis; direct immunofluorescence reveals IgA deposits in vessel walls |
| Urticarial vasculitis | Most common in adult women | Urticarial plaques that last more than 24 hours with or without purpura or hyperpigmentation; burning sensations or pain may be present | Leukocytoclastic vasculitis |
| Traumatic purpura | Children and adults | Annular ecchymosis or purpura | Hemorrhage |
| Dependent purpura in annular inflammatory disorders | Children and adults | Annular purpura on lower abdomen and legs, non-purpuric primary lesions are often present elsewhere | Dependent on the underlying disorder |
| Expanding lesions | |||
| Tinea corporis | See "Peripheral scale" above | ||
| Erythema migrans (Lyme disease) | Children and adults | Large erythematous plaque that rapidly expands | Superficial and deep lymphocytic infiltrate with plasma cells and eosinophils; spirochetes are sometimes detectable |
| Granuloma annulare | Children and adults | Non-scaly plaque with a dull erythematous color; often found on distal extremities | Palisading granulomas or interstitial histiocytes plus increased mucin |
| Superficial erythema annulare centrifugum | See "Peripheral scale" above | ||
| Deep erythema annulare centrifugum | Children and adults | Erythematous plaques without scale on face, trunk, or extremities | Superficial and deep intense perivascular lymphocytic infiltrate |
| Serum sickness-like reaction | See "Associated fever" below | ||
| Migratory | |||
| Urticaria | Children and adults | Pink edematous plaques (wheals) | Dermal edema, mild perivascular lymphocytic infiltrate with occasional eosinophils, mast cells, and neutrophils |
| Erythema marginatum | Most common in children; occurs in rheumatic fever due to group A streptococcal infection | Erythematous, polycyclic patches or plaques that migrate within hours | Superficial perivascular neutrophilic infiltrate with a few lymphocytes and eosinophils |
| Photodistributed | |||
| Subacute cutaneous lupus erythematosus | Most common in adult women; approximately 50 percent meet criteria for SLE | Erythematous, scaly plaques | Lymphocytic interface dermatitis, dermal edema, mucin |
| Lupus erythematosus tumidus | Most common in adult women | Erythematous plaques with minimal epidermal change | Superficial and deep perivascular and periadnexal lymphocytic infiltrates with mucin |
| Neonatal lupus erythematosus | Infants up to four months of age | Polycyclic erythematous plaques; may be accompanied by cardiac abnormalities | Lymphocytic interface dermatitis, dermal edema, mucin |
| Actinic lichen planus | Most common in dark-skinned young adults; particularly those of Middle-Eastern descent | Hyperpigmented plaques are often located on the face, forearms, or dorsal hands | Hyperkeratosis, hypergranulosis, interface dermatitis; similar to classic lichen planus |
| Acral | |||
| Erythema multiforme | Most frequent in young adults, but occurs at all ages; commonly associated with HSV | Target and atypical target lesions with a predilection for acral sties; mucous membrane involvement is common | Interface dermatitis, dense superficial lymphohistiocytic infiltrate in dermis, clefts and vesiculation |
| Granuloma annulare | See "Expanding lesions" above | ||
| Genital | |||
| Erythema multiforme | See "Acral" above | ||
| Circinate balanitis in reactive arthritis | Most common in young men; associated with HLA-B27 | Moist annular or serpiginous papules or erosions; also may have conjunctivitis, urethritis, and arthritis | |
| Annular lichen planus | Most common in men | Annular plaques on the penis or scrotum; may also occur on nongenital body sites | Hyperkeratosis, hypergranulosis, and interface dermatitis as in classic lichen planus; elastolysis in atrophic lesions |
| Associated fever | |||
| Acute febrile neutrophilic dermatosis (Sweet syndrome) | Most common in adult females | Erythematous, edematous, juicy plaques on upper body | Dense neutrophilic infiltrate in superficial dermis, leukocytoclasis, prominent edema |
| Serum sickness-like reaction | Children and adults; often follows antibiotic therapy | Urticarial plaques, usually slowly expanding and colliding with neighboring lesions to make polycyclic whealed plaques | Leukocytoclastic vasculitis |
| Acute hemorrhagic edema of infancy | See "Purpura" above | ||
| Kawasaki's disease | Children under the age of five | Usually an exanthematous eruption, but occasionally presents with targetoid lesions Conjunctivitis, mucositis, acral edema, and lymphadenopathy may be present | Nonspecific findings such as edema in the superficial dermis, mild perivascular lymphocytic changes; vasculitis is rare |
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