What are the differential diagnoses and management options for a male patient presenting with a genital rash?

Differential Diagnoses for Male Genital Rash

A male patient presenting with a genital rash requires systematic evaluation for sexually transmitted infections (STIs) first, followed by consideration of inflammatory dermatoses and other infectious etiologies, with laboratory confirmation essential for accurate diagnosis.

Infectious Causes (Sexually Transmitted)

Genital Herpes (HSV)

• Most common cause of sexually acquired genital ulceration 1
• 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 2
• Classic presentation: patch of redness → papules → vesicles with clear fluid → burst forming shallow ulcers → crusting and healing without scars 1
• Laboratory confirmation is essential because clinical differentiation from other causes is difficult and exclusive reliance on clinical diagnosis leads to both false positive and false negative diagnoses 1, 2
• Collect vesicular fluid with swab for viral culture, HSV DNA PCR (most sensitive), or HSV antigen detection 2
• In immunocompromised patients, can present as extensive, deep, nonhealing ulcerations rather than typical vesicles 2

Human Papillomavirus (Genital Warts)

• Visible genital warts usually caused by HPV types 6 or 11 1
• Present as papular lesions on penis, scrotum, or perianal area 3
• 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 1
• High-risk HPV types (16,18,31,33,35) associated with premalignant and malignant lesions 3

Syphilis (Treponema pallidum)

• Can present with genital ulceration 1
• Occasionally HSV and T. pallidum can be recovered from the same lesion 1
• Syphilis serology should be obtained in all patients with genital rash 1
• Secondary syphilis can present with generalized rash including genital involvement 4

Chancroid (Haemophilus ducreyi)

• Causes genital ulceration 1
• Less common but should be considered in differential of genital ulcers 1

Mpox (Monkeypox)

• Can present with erythematous umbilicated papules, vesicles and pustules with characteristic white ring 5
• Lesions may be observed simultaneously at different stages of progression on the same anatomical site 5
• Consider in travelers from endemic areas or during outbreaks 5

Infectious Causes (Non-STI)

Candidiasis (Balanitis)

• Characterized by erythematous areas on glans penis with pruritus or irritation 1
• More common in uncircumcised men and those with diabetes 1
• Male sex partners of women with recurrent vulvovaginal candidiasis may develop symptomatic balanitis 1

Scabies

• Transmitted by skin-to-skin contact; sexual transmission common 3
• Penis and scrotum are favorite locations for scabious lesions 3

Pediculosis (Pubic Lice)

• Transmitted by skin-to-skin contact; sexual transmission common 3

Inflammatory/Dermatologic Causes

Psoriasis

• May have atypical appearance in genital area 3
• Typical psoriatic scale usually not apparent due to moisture and maceration 3

Lichen Planus

• May have atypical appearance in genital area 3

Contact Dermatitis (Allergic or Irritant)

• Allergic: may result from condoms, lubricants, feminine hygiene products, spermicides 3
• Irritant: more common, resulting from persistent moisture and maceration 3

Lichen Sclerosus

• Chronic inflammatory disease presenting as atrophic white patches on glans penis and foreskin 3
• Common cause of phimosis in uncircumcised men 3
• Involvement of urethral meatus may lead to progressive meatal stenosis 3

Plasma Cell Balanitis (Zoon's Balanitis)

• Benign, idiopathic condition presenting as solitary, smooth, shiny, red-orange plaque of glans and prepuce 3
• Typically in middle-aged to older men 3

Non-Infectious Mimics

Fixed Drug Eruption

• Can cause mucosal ulcerations that may be confused with genital herpes 1

Behçet Syndrome

• Mucosal ulcerations associated with this condition may mimic genital herpes 1

Inflammatory Bowel Disease (Crohn Disease)

• Can cause genital ulceration 1

Herpes Zoster (Shingles)

• Can occur in genital region and may be misdiagnosed as genital herpes 6
• Vesicles contain clear fluid, burst forming shallow ulcers that crust and heal without scarring 6

Premalignant/Malignant Conditions

Squamous Cell Carcinoma In Situ

• Erythroplasia of Queyrat and Bowen's disease cannot be excluded clinically 3
• Biopsy required to confirm diagnosis 3
• Apparent clinical benignity may lead to lengthy periods of misdiagnosis 3

Squamous Cell Carcinoma

• Most common malignancy of penis 3
• Role of oncogenic HPV types established 3

Essential Diagnostic Approach

Initial Evaluation

• Obtain sexual history including recent contacts within 60 days 1
• Document lesion characteristics: vesicular, ulcerative, papular, location, distribution 1
• Assess for systemic symptoms: fever, lymphadenopathy, dysuria 1

Laboratory Testing

• Swab vesicular fluid or ulcer base for HSV PCR, viral culture, or antigen detection 1, 2
• Syphilis serology 1
• HIV counseling and testing 1
• Gram stain and culture of urethral exudate if urethritis suspected 1
• Nucleic acid amplification test for N. gonorrhoeae and C. trachomatis 1
• Consider biopsy if diagnosis uncertain, lesions don't respond to therapy, or malignancy suspected 1, 3

Critical Pitfalls to Avoid

• Do not rely on clinical diagnosis alone for herpes—laboratory confirmation essential 1, 2
• Do not assume all genital ulcers are herpes—consider syphilis, chancroid, and non-infectious causes 1
• Do not miss immunocompromised status—atypical presentations more common in HIV-positive patients 2
• Do not forget to test for concurrent STIs—multiple infections can coexist 1
• Do not delay biopsy if lesions are pigmented, indurated, fixed, ulcerated, or non-responsive to therapy—malignancy must be excluded 1, 3