Mpox Presenting as Anorectal Disease: Clinical Recognition and Diagnosis

Mpox, a viral zoonosis caused by the monkeypox virus, has increasingly presented with primary anorectal symptoms, including proctitis, severe rectal pain, and tenesmus. According to the Centers for Disease Control and Prevention (CDC), while mpox traditionally manifests as a systemic febrile illness with a characteristic rash, recent outbreaks have shown a significant shift toward localized genital and anorectal lesions, often occurring in the absence of classic prodromal symptoms like fever or lymphadenopathy.

Clinical Presentation of Anorectal Mpox

Anorectal mpox often mimics other sexually transmitted infections (STIs), which can lead to diagnostic delays. Patients frequently present with intense anal pain, rectal bleeding, and the sensation of needing to pass stool even when the rectum is empty, known as tenesmus. Physical examination often reveals proctitis—inflammation of the rectal lining—and visible ulcerations or pustules in the perianal area.

The World Health Organization (WHO) notes that these lesions can be easily confused with herpes simplex virus (HSV), syphilis, or gonorrhea. Because the clinical presentation is highly variable, clinicians are advised to maintain a high index of suspicion for mpox in patients presenting with acute proctitis, particularly if the lesions do not respond to standard STI treatments.

Diagnostic Approach and Testing

Accurate diagnosis of mpox requires molecular testing, specifically via polymerase chain reaction (PCR). The CDC recommends that clinicians collect specimens directly from lesions, such as swabs of the ulcer base or crusts, for orthopoxvirus DNA testing.

Because coinfections are common, testing for other STIs—including HIV, syphilis, gonorrhea, and chlamydia—remains a critical component of the clinical workup. A positive result for another STI does not rule out mpox; clinicians should screen for both simultaneously when the patient’s history and symptoms warrant it.

Managing Mpox Symptoms

Most cases of mpox are self-limiting, with symptoms typically resolving within two to four weeks. However, the pain associated with anorectal involvement can be severe and may require targeted management. Treatment strategies often focus on supportive care, including pain management and the maintenance of hydration.

In specific cases, particularly for patients with severe disease or those at high risk for complications, the antiviral medication tecovirimat (TPOXX) may be considered. According to the National Institute of Allergy and Infectious Diseases (NIAID), tecovirimat inhibits the virus by targeting the VP37 protein, which is essential for the dissemination of the virus within the host.

Key Considerations for Patients

• Symptom Awareness: Seek medical evaluation if you develop unexplained rectal pain, anal lesions, or proctitis.
• Transmission: Mpox spreads through close, personal, often skin-to-skin contact, including direct contact with infectious rashes, scabs, or body fluids.
• Prevention: Vaccination with the JYNNEOS vaccine is recommended for individuals at high risk of exposure to mpox.
• Isolation: Patients diagnosed with mpox should isolate until all lesions have crusted over and a fresh layer of skin has formed.

Early identification of mpox remains the most effective tool for limiting transmission and managing patient discomfort. Clinicians should prioritize a thorough physical examination and PCR testing for any patient presenting with persistent anorectal symptoms that deviate from the expected course of common STIs.