Erosive lesions with oat-flake-like scaling in a seborrheic pattern

Question

What is the diagnosis?

Answer

Diagnosis: Secondary syphilis.

Discussion

The diagnosis of secondary syphilis was confirmed with positive immunohistochemical (IHC) staining using anti-Treponema pallidum antibody [Figure 4]. The non-treponemal test (RPR) was positive (1:16) and confirmed by a treponemal test. Serologies for HCV, HBV, and HIV were negative.

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Figure 4:

Immunohistochemical staining using anti-Treponema pallidum antibody, 60x.

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The patient received treatment with a single dose of 2.4 million units of intramuscular benzathine penicillin, which led to complete resolution of lesions within one month. The non-treponemal test (RPR) became negative after 6 months.

Syphilis is a sexually transmitted infection caused by the spirochete Treponema pallidum subs. pallidum. Its prevalence has increased notably in recent years, particularly among men who have sex with men and HIV-positive individuals.

The clinical presentation of secondary syphilis is highly variable, the most common being a diffuse, non-pruritic, papulosquamous rash, along with lymphadenopathy.¹ It typically affects the palms and soles and may be associated with flu-like prodromal symptoms. The mucous membranes may be unaffected or present erosive lesions. In HIV-positive patients, nodular or ulcerative lesions (malignant syphilis) are more common.² Our patient presented with erosive lesions with oat-flake-like scaling in a seborrheic distribution, without systemic or mucosal involvement, resembling pemphigus foliaceus. Although a wide spectrum of syphilitic manifestations has been reported in the literature, generalised erosive lesions are uncommon, particularly in HIV-negative patients. These lesions can mimic other conditions, including subcorneal pustular dermatosis, pemphigus foliaceous, subacute cutaneous lupus erythematosus, seborrheic dermatitis, bullous impetigo, or lymphomatoid papulosis.

While laboratory tests generally confirm the diagnosis of secondary syphilis, histology can be highly useful in certain cases, such as HIV-positive cases or those with atypical clinical presentations. Macular lesions are characterised by a sparse perivascular lymphohistiocytic infiltrate with few plasma cells. In papular lesions, the infiltrate may appear as a band with abundant plasma cells and epidermal changes such as parakeratosis, acanthosis, spongiosis, and exocytosis. Some of these findings may resemble other entities such as lymphomatoid papulosis or other lymphoproliferative disorders; however, the distribution of the infiltrate, assessment of cellular clonality, and the immunophenotypic profile are essential steps for establishing the correct differential diagnosis. According to Flamm et al.³ the most frequent histologic findings of secondary syphilis include an interstitial inflammatory pattern, endothelial oedema, irregular acanthosis, and elongation of epidermal ridges. The localisation of spirochetes, either with silver staining techniques or anti-T. pallidum antibodies, help determine the infection stage; they populate the epidermis in perivascular distribution in primary syphilis and extensively in the epidermis in secondary syphilis.^4,5

We report an unusual manifestation of secondary syphilis in an HIV-negative patient, presenting as erosions and crusts in a seborrheic distribution. It is essential to consider syphilis among the differentials for such lesions, to avoid diagnostic delays and inadequate treatments.