Differentials

Secondary syphilis

SIGNS / SYMPTOMS
INVESTIGATIONS
SIGNS / SYMPTOMS

Palmoplantar involvement common, orientation of lesions more random, possible history of primary genital ulcer, positive risk factors.[2][3][9]

INVESTIGATIONS

Rapid plasma reagin/Venereal Disease Research Laboratory serology positive.

Syphilis infection

Guttate psoriasis

SIGNS / SYMPTOMS
INVESTIGATIONS
SIGNS / SYMPTOMS

Usually follows streptococcal infection, small erythematous papules with micaceous white scale, no particular orientation.[3][23]

INVESTIGATIONS

Antistreptolysin O titres positive.

Skin biopsy will demonstrate regular acanthosis and hypergranulosis.

Psoriasis

Tinea corporis

SIGNS / SYMPTOMS
INVESTIGATIONS
SIGNS / SYMPTOMS

Usually single or few lesions, may resemble herald patch. No prodromal symptoms, no subsequent eruption.[3][23]

INVESTIGATIONS

Fungal culture positivity, hyphae on potassium hydroxide (KOH) preparation.

Dermatophyte infections

Drug eruption

SIGNS / SYMPTOMS
INVESTIGATIONS
SIGNS / SYMPTOMS

Rash between 5 and 20 days after initiating medicine, protracted course, no herald patch, lesions more likely to be bright red or violet, pruritus severe.[7]

Medication history including recent use of: ACE inhibitors, aspirin (acetylsalicylic acid), allopurinol, arsenics, barbiturates, beta-blockers, bismuth, clonidine, d-penicillamine, gold, hydrochlorothiazide, isotretinoin, levamisole, meprobamate, methopromazine, metronidazole, nimesulide, non-steroidal anti-inflammatory drugs, omeprazole, sulfasalazine, terbinafine, tyrokinase kinase inhibitors, diphtheria toxoid, BCG/hepatitis B virus/pneumococcal vaccines.[2][3][6][7][23][24][25][26]

INVESTIGATIONS

Histopathology more consistent with drug eruption-increased dermal eosinophils.[25]

Common cutaneous drug reactions

Nummular eczema

SIGNS / SYMPTOMS
INVESTIGATIONS
SIGNS / SYMPTOMS

Lesions are discrete, round, more likely to have generalised scale rather than collarette, usually xerotic.[3][24]

INVESTIGATIONS

Clinical diagnosis.

Atopic dermatitis

Pruritic urticarial papules and plaques of pregnancy

SIGNS / SYMPTOMS
INVESTIGATIONS
SIGNS / SYMPTOMS

Discrete pruritic papules and plaques over trunk in primigravida pregnant women in the third trimester, usually predilection for striae; sparing of umbilicus; no herald patch.[20]

INVESTIGATIONS

Clinical diagnosis.

Pityriasis lichenoides chronica

SIGNS / SYMPTOMS
INVESTIGATIONS
SIGNS / SYMPTOMS

Longstanding eruption of flat-topped papules with fine scale, no particular orientation, duration months or longer; no herald patch.[3]

INVESTIGATIONS

Clinical diagnosis.

Pityriasis lichenoides

Pityriasis (tinea) versicolor

SIGNS / SYMPTOMS
INVESTIGATIONS
SIGNS / SYMPTOMS

Minimal fine scale, salmon pink to hypopigmented to hyperpigmented macules confluent into patches over chest and back. No herald patch. More central and superiorly located, no skin cleavage line predilection, minimal to no pruritus.

INVESTIGATIONS

Spores and hyphae on KOH preparation.

Pityriasis versicolor

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