Differential Diagnosis for a 27-year-old Male with Small Round Spots on the Penis

Single Most Likely Diagnosis

• Genital warts (Condylomata acuminata): Given the recent sexual intercourse and the description of small round spots under the foreskin and on the head of the penis, genital warts are a strong consideration. They are a common sexually transmitted infection (STI) caused by the human papillomavirus (HPV), often presenting as small, flesh-colored or gray swellings in the genital area.

Other Likely Diagnoses

• Molluscum contagiosum: This is a viral infection that causes small, pearly, or flesh-colored bumps. It's contagious and can be spread through sexual contact, making it a plausible diagnosis given the patient's recent sexual activity.
• Fordyce spots: These are small, yellowish or white bumps on the penis or scrotum that are caused by the abnormal presence of sebaceous glands in the skin. They are benign and common, but their appearance can sometimes cause concern.
• Pearly penile papules: These are small, dome-shaped bumps that are found on the corona of the glans penis. They are a normal anatomical variation and are not associated with any disease or infection.

Do Not Miss Diagnoses

• Primary syphilis: The presentation of a single, painless chancre (ulcer) at the site of inoculation is characteristic of primary syphilis. Although the patient's spots are described as multiple and without pain, swelling, or itching, syphilis is a critical diagnosis not to miss due to its potential for serious complications if left untreated.
• Genital herpes: Typically presents with painful blisters or ulcers, but atypical presentations can occur. Given the potential severity of genital herpes and its implications for sexual health, it's essential to consider this diagnosis.

Rare Diagnoses

• Lichen nitidus: A rare skin condition characterized by tiny, shiny, flat-topped bumps that can appear on the genitals among other areas. It's usually asymptomatic and can be confused with other conditions.
• Bowenoid papulosis: A rare condition associated with HPV infection, presenting as flat, reddish-brown lesions on the genital area. It's considered a form of intraepithelial neoplasia and has the potential for malignant transformation, making it an important, though rare, diagnosis to consider.