Arthritis due to monkeypox virus: A case report

Since the beginning of May 2022, an outbreak of monkeypox virus infection is occurring worldwide [1], [2]. Typical clinical presentation consists in flu-like syndrome with pustular skin eruption. Rarer presentations and complications include solitary skin lesion, rectal perforation, penile swelling, oropharyngeal manifestations, pneumonia, encephalitis, keratitis and secondary bacterial infections [3], [4], [5], [6].

Here we report an unusual case of monkeypox virus arthritis.

A 39-year old man presented with fever, genital ulcers, diffuse arthralgias and painful left knee swelling. He reported unprotected sexual intercourse with a casual male partner 11 days earlier but no recent travel nor prior antibiotic intake. Past medical history included secondary syphilis, Chlamydia trachomatis and Neisseria gonorrhoeae urethritis, and intermittent oral emtricitabine and tenofovir disoproxil for human immunodeficiency virus (HIV) pre-exposure prophylaxis (PrEP).

Physical examination disclosed 38 °C temperature, left knee arthritis without other synovitis, orchitis with penile shaft swelling, tender inguinal lymphadenopathy, ulcerated lesion on the penis, and 10 vesiculopapular lesions across the pubis, arms, chest and scalp (Fig. 1 ).

Fig. 1.

Ulcerated lesion with penile swelling.

Left knee arthrocenthesis revealed purulent fluid (cell count was not feasible). Treatment included intramuscular injection of benzathine-benzylpenicillin and 7-day intravenous ceftriaxone (2 g per day).

Blood cultures, urinary and anal C. trachomatis PCR, HIV and hepatitis C serologies were negative. N. gonorrhoeae PCR was positive on throat sample. Syphilis rapid plasma reagin (RPR) was reactive (dilution of 1:2) suggesting possible syphilis reinfection or incomplete serologic response. Skin lesions and synovial fluid monkeypox PCR were positive for West African monkeypox virus clade (cycle threshold 30.03 in synovial fluid corresponding to low viral load). Synovial fluid analyses were negative for crystal identification, Gram stain, bacterial and mycobacterial cultures, N. gonorrhoeae PCR and specific culture.

At 15-day follow-up arthritis improved greatly, lymphadenopathies resolved and 50% of skin lesions were crusted (Fig. 2 ). After two months, only remained the genital ulcer.

Fig. 2.

Healed skin lesion on the right buttock.

To our knowledge, this is the first reported case of monoarthritis due to monkeypox virus. It has several differential diagnoses. We ruled out arthritis due to pyogenic bacteria by synovial analyses: sterile culture in the absence of prior antibiotherapy and negative PCR and culture for N. gonorrhoae. Other diagnoses were unlikely: reactive arthritis because of absent recent chlamydia infection, short delay between possible contamination and symptoms, and rapid resolution of symptoms without anti-inflammatory treatment, rheumatic disease because of the absence of former arthritis or extra-articular symptoms and crystallyne arthritis because of absence of crystals in joint fluid, patient's age and absence of risk factor for gout or chondrocalcinosis.

Real-time PCR Monkeypox molecular testing has good sensitivity and specificity [7]. Absence of skin lesions on the patient's legs made unlikely iatrogenic positive PCR by contiguous spread of the virus. However, we could not completely exclude joint puncture contamination by blood.

Historic case reports of smallpox arthritis have described purulent synovial fluid [8], [9], suggesting this could be a characteristic of orthopoxvirus infections.

This case report encourages clinicians to pay attention to arthritis of unknown etiology, as it could be due to monkeypox virus, especially in the appropriate clinical and epidemiological context.

Disclosure of interest

The authors declare that they have no competing interest.