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Case: Petaloid Dermatosis Affecting the Scalp and Genitalia

Consider secondary syphilis in the differential of annular lesions

petaloid dermatoses

By Taylor Bullock, MD, Shruti Agrawal, MD, and Wilma Bergfeld, MD


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A 41-year-old-male presented with a one-month history of pruritic lesions on his scalp, neck and penis. He had attempted a two-week course of terbinafine cream, with no improvement. The lesions were unaffected by exposure to sunlight. The patient also reported new-onset wrist stiffness and pain. He had been diagnosed with primary syphilis nine months before presentation, with a reactive plasma reagin titer of 1:64, and had been treated with intramuscular penicillin G benzathine 2.4 million units.

Physical examination revealed annular and petaloid plaques with central clearing and raised borders
on the scalp, right mandibular angle and penis. No lesions were observed on the oral mucosa, palms, or soles. No lymphadenopathy or new-onset alopecia was present.

Clinically, the differential diagnosis included discoid lupus erythematosus, lichen planus, tinea infection, sarcoidosis and annular secondary syphilis. Serology for human immunodeficiency virus was nonreactive, and cutaneous punch biopsy of the mandibular lesion was performed.

Histologic sections revealed numerous plasma cells within the superficial dermis to the mid-dermis. Staining for Treponema pallidum highlighted numerous spirochetes, consistent with syphilis. Repeat rapid plasma reagin testing was positive with a 1:256 titer.

Though we are not certain, we believed that this patient likely acquired a new case of syphilis after treatment of his previous infection, because he presented at nine months after the primary diagnosis, and resolution of secondary syphilis typically occurs within 12 weeks.1 Therefore, he was given an intramuscular dose of 2.4 million units of penicillin G benzathine, with close follow-up recommended with the department of infectious diseases.

Secondary syphilis and other petaloid dermatoses

Syphilis is a sexually transmitted disease caused by the spirochete bacterium T pallidum. While primary syphilis typically presents as a solitary, painless papule or ulcer in the genital area, secondary syphilis is a generalized infection often accompanied by systemic symptoms such as fever, malaise, headaches, sore throat or joint pain.1 These acute symptoms typically begin six to eight weeks after the appearance of the primary lesion and resolve within 12 weeks.1


The most common cutaneous presentation of secondary syphilis is a generalized morbilliform rash, usually involving the palms and soles.2 However, secondary syphilis can present as annular secondary syphilis, which is also known as petaloid syphilis, owing to its resemblance to the petals of a flower.2 Lesions in annular secondary syphilis often occur close to the angle of the mandible and frequently spare the palms and soles.3–5 Secondary syphilis typically presents without
lymphadenopathy and often affects the genitalia.5

Management of petaloid dermatoses

The differential diagnosis for annular plaques is broad and depends on clinical history, symptoms and location and morphology of the lesions. Annular lesions on the head and neck could also be secondary to petaloid seborrheic dermatitis, tinea corporis, discoid lupus erythematosus, subacute lupus erythematosus, cutaneous sarcoidosis, or granuloma annulare.

A thorough history and physical examination, relevant laboratory studies, skin biopsy, and potassium
hydroxide preparation of these lesions are helpful in narrowing the diagnosis.

It is important for clinicians to consider petaloid secondary syphilis in the differential of annular lesions, as it can mimic other inflammatory and infectious etiologies.

This article is adapted and republished from the Cleveland Clinic Journal Of Medicine, (2023; 90[9]: 527-528).


  1. Lautenschlager S. Cutaneous manifestations of syphilis: recognition and management. Am J Clin Dermatol 2006; 7(5):291–304.
  2. Meffert JJ. Photo quiz. Flowering dermatosis. Am Fam Physician 1998; 57(11):2805–2806.
  3. Qian YT, Ma DL. Pruritic annular concentric plaques. BMJ 2019; 367:l5512.
  4. Guillén BF, von der Weth MMG, Oñate CV, Tapial JM, Bel PH. Secondary syphilis as a single annular plaque on the penis mimicking granuloma annulare. Indian J Dermatol Venereol Leprol 2021;87(3):438.
  5. Zhao CC, Zhang Z, Zheng S, Li J-H. Annular secondary syphilis on the penis: a case report. Int J Dermatol and Venereol 2019; 2(2):118–119.


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