We read with great interest the comment by Dr Mungmunpuntipantip and Dr Wiwanitkit on our paper entitled « Arthritis due to monkeypox virus: A case report ».
We presented an unusual case of purulent arthritis due to monkeypox virus associated with typical cutaneous lesions. We agree with the authors that cutaneous lesions are useful for diagnostic orientation in case of arthritis. However, monkeypox skin lesions are not necessarily typical and can be strictly localized to non-noticeable places like the anal canal thus complicating diagnostic challenge.
We concur that molecular diagnosis is essential in case of atypical presentation like arthritis. On such cases, real-time Polymerase Chain Reaction (PCR) should be performed on skin lesions if present, on pharyngeal or rectal swabs or even on joint fluid depending on the symptoms. Real-time monkeypox PCR assays are highly sensitive and specific [1]. Even if false positive results are always possible, the Center for disease control (CDC) recommends to resample and retest positive sample with late cycle threshold value (> 34) in order to improve specificity [2]. This is what has been done in our laboratory. The pretest probability is also important to acknowledge for data interpretation.
Our case report is the first reported case of neutrophilic arthritis due to monkeypox virus, which is of particular interest since this is very uncommon for viral arthritis. The case published by Dr Fonti et al. is a lymphocytic arthritis due to monkeypox virus [3]. To note, the patient described in this case report also had associated osteomyelitis. There are indeed a few reports of purulent arthritis and osteomyelitis due to other orthoxpoxviruses sometimes associated with bone distortion or pathologic fractures [4], [5]. We believe that this case report, while depicting a rare phenomenon, should be taken into account specially to pay attention to long-term articular outcome of these patients.
Disclosure of interest
The authors declare that they have no competing interest.
References
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