In a 69-year-old man with a 3–4‑day pustular rash on the face, neck, and buttocks, no systemic symptoms, recent travel to Japan, and recent men‑who‑have‑sex‑with‑men (MSM) exposure, what work‑up, differential diagnosis, and treatment are indicated?

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Pustular Rash in MSM with Recent Japan Travel: Workup, Differential, and Treatment

This patient requires immediate evaluation for emerging sexually transmitted dermatophilosis, mpox, and disseminated gonococcal infection, with empiric treatment for gonorrhea/chlamydia while awaiting confirmatory testing.

Immediate Workup

Skin Lesion Evaluation

  • Swab pustular lesions for:
    • Bacterial culture (including Dermatophilus congolensis)
    • Mpox PCR testing
    • HSV PCR
    • Gram stain and routine bacterial culture
  • Skin biopsy of representative pustule if diagnosis unclear after initial testing

Sexual Health Screening

  • Urethral/rectal swabs for N. gonorrhoeae and C. trachomatis by NAAT 1
  • Blood cultures if any systemic symptoms develop
  • HIV testing (4th generation antigen/antibody) 2
  • Syphilis serology (RPR/VDRL with reflex treponemal testing) 2

Additional Testing

  • Complete blood count with differential
  • Comprehensive metabolic panel
  • Consider anorectal examination if any anal symptoms present

Differential Diagnosis (Prioritized by Likelihood)

1. Dermatophilosis (Emerging STI)

The most critical consideration given recent Japan travel and MSM activity. Recent 2026 reports document sexually transmitted Dermatophilus congolensis clusters among MSM in France, Sweden, and Japan 3, 4. This traditionally zoonotic pathogen now shows clear evidence of human sexual transmission within MSM networks, particularly in travelers to Japan 4.

Key features:

  • Pustular lesions on face, neck, buttocks (matches this patient)
  • No animal contact required
  • Genomically linked clusters in sexual networks
  • Often misdiagnosed initially

2. Mpox

Presents with pustular lesions in MSM, can involve face and anogenital areas 5. The 2022-ongoing outbreak shows atypical presentations, especially in MSM and HIV-positive individuals 6. Concurrent acute HIV infection can complicate presentation 5.

3. Disseminated Gonococcal Infection (DGI)

Pustular or petechial acral skin lesions with asymmetric arthralgia 1, 7. However, quinolones cannot be used in MSM or those with recent foreign travel due to quinolone-resistant N. gonorrhoeae (QRNG) prevalence 1.

4. Secondary Syphilis

Can present with pustular lesions, though typically more papulosquamous.

5. Folliculitis (bacterial or fungal)

Less likely given distribution pattern and sexual exposure history.

Empiric Treatment Strategy

Immediate Empiric Therapy (Start Today)

For presumptive gonorrhea/chlamydia (given MSM status and travel):

  • Ceftriaxone 125 mg IM single dose 1
  • PLUS Doxycycline 100 mg PO twice daily for 10 days 1

Critical caveat: Do NOT use quinolones (ciprofloxacin, ofloxacin, levofloxacin) in this patient due to MSM status and recent Japan travel—high QRNG prevalence 1.

If Dermatophilosis Confirmed

  • Penicillin-based antibiotics are typically effective for Dermatophilus species
  • Consult infectious disease specialist for specific dosing
  • Monitor for treatment response over 3-7 days

If Mpox Confirmed

  • Supportive care for most cases
  • Consider tecovirimat (TPOXX) if severe disease or immunocompromised
  • Isolate patient and implement contact precautions
  • Report to public health authorities

If DGI Confirmed

  • Hospitalize for initial IV therapy 1, 7
  • Ceftriaxone 1 g IV/IM every 24 hours until 24-48 hours after improvement 1
  • Then switch to cefixime 400 mg PO twice daily to complete ≥1 week total 1

Critical Follow-Up Actions

Partner Management

  • Notify all sexual contacts within 60 days 1, 2
  • Partners require evaluation and empiric treatment
  • Instruct patient to abstain from sexual activity until treatment completed and symptoms resolved 1

Reassessment Timeline

  • 3 days: If no improvement, reconsider diagnosis 2, 7
  • 1 week: Review all culture and PCR results
  • 3 months: Repeat HIV and syphilis testing if initially negative 2

Common Pitfalls to Avoid

  1. Do not dismiss as simple folliculitis in MSM with travel history—emerging STIs like dermatophilosis are under-recognized 4

  2. Never use quinolones in MSM or recent international travelers for presumed gonorrhea 1

  3. Do not delay mpox testing even without typical monkeypox appearance—atypical presentations are common in MSM 6, 5

  4. Test for acute HIV infection using 4th generation assay or HIV RNA, as concurrent acute HIV with mpox or other STIs can occur 5

  5. Obtain proper specimens before starting antibiotics when possible, but do not delay empiric treatment

References

1
Guideline

sexually transmitted diseases treatment guidelines, 2006.

MMWR Recommendations and Reports, 2006

4
Research

Dermatophilosis among men who have sex with men, Stockholm, Sweden, March to June, 2026.

Euro surveillance : bulletin Europeen sur les maladies transmissibles = European communicable disease bulletin, 2026

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This information is intended for healthcare professionals. Any medical decision-making should rely on clinical judgment and independently verified information. The content provided herein does not replace professional discretion and should be considered supplementary to established clinical guidelines. Healthcare providers should verify all information against primary literature and current practice standards before application in patient care. Dr.Oracle assumes no liability for clinical decisions based on this content.