Differential Diagnoses for Male Genital Rash

Infectious Causes

The Centers for Disease Control and Prevention recommends that a male patient presenting with a genital rash should be evaluated for sexually transmitted infections (STIs) first, followed by consideration of inflammatory dermatoses and other infectious etiologies, with laboratory confirmation essential for accurate diagnosis, as most common cause of sexually acquired genital ulceration is Genital Herpes (HSV) 1, 2
Genital Herpes (HSV) presents with vesicular lesions that progress to shallow ulcers, though most persons have mild and atypical lesions that cannot be diagnosed by physical examination alone, and laboratory confirmation is essential because clinical differentiation from other causes is difficult 1, 3
The Centers for Disease Control and Prevention notes that Human Papillomavirus (Genital Warts) usually caused by HPV types 6 or 11, and biopsy rarely needed unless diagnosis uncertain, lesions don't respond to therapy, disease worsens during therapy, patient immunocompromised, or warts are pigmented, indurated, fixed, and ulcerated 4, 5
Syphilis (Treponema pallidum) can present with genital ulceration, and occasionally HSV and T. pallidum can be recovered from the same lesion, and syphilis serology should be obtained in all patients with genital rash 1, 4, 5

Fixed Drug Eruption can cause mucosal ulcerations that may be confused with genital herpes, and Behçet Syndrome mucosal ulcerations associated with this condition may mimic genital herpes 1, 2
Inflammatory Bowel Disease (Crohn Disease) can cause genital ulceration, and Herpes Zoster (Shingles) can occur in genital region and may be misdiagnosed as genital herpes 1, 2, 6

The Centers for Disease Control and Prevention recommends obtaining sexual history including recent contacts within 60 days, and document lesion characteristics: vesicular, ulcerative, papular, location, distribution 4, 5, 7, 1
Swab vesicular fluid or ulcer base for HSV PCR, viral culture, or antigen detection, and syphilis serology, and HIV counseling and testing should be performed 7, 1, 3, 4, 5
Gram stain and culture of urethral exudate if urethritis suspected, and nucleic acid amplification test for N. gonorrhoeae and C. trachomatis should be considered 4, 5
Biopsy should be considered if diagnosis uncertain, lesions don't respond to therapy, or malignancy suspected 4

In men, lichen sclerosus most commonly affects the glans, coronal sulcus, frenulum, and prepuce, and rarely involves the penile shaft. 8
Unlike in females, pruritus is not a prominent symptom of male genital lichen sclerosus, even when white atrophic patches are present. 9
Consequently, when a patient presents with an itchy penile shaft, lichen sclerosus should be considered unlikely unless characteristic porcelain‑white patches extend from the glans onto the shaft. 8

Any indurated, fixed, pigmented, or ulcerated lesion on the penis warrants a biopsy to exclude squamous cell carcinoma. 10