P036 Two cases of annular erythema and malignancy: erythema gyratum repens and extensive tinea corporis in an immunosuppressed patient on methotrexate

Abstract

Two cases of annular erythema are described to illustrate how a shared morphological pattern can reflect markedly different underlying pathologies: one a paraneoplastic dermatosis, and the other steroid-modified extensive tinea corporis in an immunosuppressed patient with a history of malignancy. We present the cases, discuss the diagnoses and outline the relevant clinicopathological considerations. Case 1 describes a 78-year-old man with a 3-month history of a widespread annular, gyrate erythematous eruption with trailing scale. The rash progressed over weeks from the trunk to the proximal limbs. The clinical appearances were characteristic of erythema gyratum repens. A skin biopsy showed nonspecific epidermal hyperplasia with mild chronic inflammatory infiltrate and small-vessel proliferation. Computed tomography imaging of the thorax, abdomen and pelvis identified a large left-upper-lobe lung mass, subsequently histologically confirmed as non-small cell carcinoma, staged T3N1M0. The patient was managed with best supportive care. Case 2 describes a 29-year-old man with Fitzpatrick skin type V and a past medical history of papillary thyroid carcinoma, who presented with a 3-month history of widespread hyperkeratotic plaques and a scaly erythematous scalp, consistent with psoriasis. Oral methotrexate was commenced following inadequate response to topical treatments. The eruption evolved into extensive annular erythema with peripheral scale, dusky hyperpigmentation and focal pustulation. Tender induration and hyperpigmentation were particularly evident over the ears, face and lower limbs. Differential diagnoses included toxic migratory erythema, erythema gyratum repens and tinea corporis. Skin biopsy showed focal hyperkeratosis and parakeratosis, and a nonspecific mild superficial perivascular lymphocytic infiltrate. Skin mycology was positive for Trichophyton mentagrophytes, with clinical resolution following oral terbinafine. These cases highlight the breadth of annular erythema presentations across age groups, skin types and disease processes, and emphasize the importance of vigilance during triage and evaluation of annular eruptions, particularly in patients with skin of colour.