Intended for healthcare professionals

Endgames Case Review

Atypical psoriasis

BMJ 2015; 351 doi: (Published 04 November 2015) Cite this as: BMJ 2015;351:h5510
  1. Saskia Ingen-Housz-Oro, dermatologist12,
  2. Françoise Foulet, mycologist34,
  3. Olivier Chosidow, professor of dermatology1245
  1. 1Service de Dermatologie, AP-HP, Henri Mondor Hospital, Créteil, France
  2. 2EA 7379-EpiDermE (Epidémiologie en Dermatologie et Evaluation des Thérapeutiques), Créteil, France
  3. 3Laboratoire de Mycologie, AP-HP, Henri Mondor Hospital
  4. 4Université Paris-Est Val de Marne Créteil UPEC, Créteil
  5. 5Centre d’Investigation Clinique 1430, AP-HP, Créteil
  1. Correspondence to: S Ingen-Housz-Oro saskia.oro{at}

A 34 year old woman presented with an extensive cutaneous eruption on the lower limbs and buttocks. She had had atopic dermatitis with recurrent flares until age 22. She currently had idiopathic hirsutism and chronic foot onychodystrophy. Results of fungal culture of the nails three years earlier were negative. She had no personal or family history of psoriasis and no pets. When the lesions first appeared on her knees six months earlier she had consulted her general practitioner. A diagnosis of psoriasis was suspected and daily topical calcipotriol and betamethasone (strength III—potent topical steroid) were prescribed. The treatment was continued even though the lesions worsened and extended to her thighs and buttocks, with intense pruritus and burning. Finally she consulted our dermatological emergency unit.

She had multiple, widespread, pruritic, mostly well demarcated, erythematous plaques on the knees (fig 1A), thighs, and buttocks. There were disto-lateral modifications of the nails of both big toes, with white-yellow coloration (xanthonychia), thickening of the nail plate (pachyonychia), and distal onycholysis (fig 1B). Her general condition was otherwise normal, including no fever.


  • 1. What is your diagnosis and what history and clinical findings suggest this?

  • 2. What is the best laboratory test to confirm the diagnosis?

  • 3. How should the patient be treated?


1. What is your diagnosis and what history and clinical findings suggest this?

Short answer

Tinea incognito, an atypical extensive dermatophytosis (tinea corporis) often seen with chronic use of topical steroids.


The clinical presentation—well demarcated, erythematous plaques surrounded by a microvesicular and desquamative border—suggested extensive dermatophytosis (tinea corporis; fig 2). However, in some places, such as the knees (fig 1A), the lesions were more atypical and symmetrical, mimicking eczema or psoriasis (tinea corporis lesions are usually asymmetrical). Close examination of the feet in this patient, who reported a history of onychodystrophy, identified disto-lateral modifications of the nails of both big toes—white-yellow coloration (xanthonychia) and thickening …

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