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Skin-nontumor / Clinical Dermatology

Other dermatoses

Pityriasis rosea

Reviewer: Mowafak Hamodat, MB.CH.B, MSc., FRCPC, Eastern Health, St. Johns, Canada (see Reviewers page)
Revised: 1 August 2011, last major update August 2011
Copyright: (c) 2002-2011, PathologyOutlines.com, Inc.

Definition
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● Initially a single large “herald” patch, then a generalized rash 1-2 weeks later, lasting 2-6 weeks
● Self-limited, possibly viral, benign lesion of children and young adults
● Associated with pyrexia, headache, malaise, lymphadenopathy
● Seasonal variation
● Pityriasis means "fine scales"

Clinical description
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● Papulosquamous lesions of trunk and extremities
● Herald patch: single red scaly lesion that increases in size over 48 hours up to 2-10 cm

Clinical images
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Lesions on chest

Micro description
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● Non-specific subacute or chronic dermatitis with focal hyperkeratosis and angulated parakeratosis with slight acanthosis
● Granular cell layer is absent beneath the foci of parakeratosis
● Intraepidermal cytoid body may be present
● Focal acantholytic dyskeratosis occasionally documented
● Also lymphohistiocytic infiltrate around vessels of superficial plexus and slight spongiosis
● Occasionally scattered eosinophils and erythrocytes within epidermis

Differential diagnosis
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● Guttate psoriasis: has neutrophils within parakeratotic mounds
● Drug reaction: large number of eosinophils
● Acute and subacute eczematous dermatitis: lacks lens shaped parakeratosis and limited spongiosis
● Pityriasis lichenoides chronica: interface change, vacuolar degeneration of basal layer of epidermis
● Fungal infections: PAS stains dermatophytes
● Syphilis, secondary: skin lesions may be similar, but different clinical history and histology

Additional references
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● eMedicine

End of Skin-nontumor / Clinical Dermatology > Other dermatoses > Pityriasis rosea

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