# Pyomyositis of the obturator internus muscle

Théo Renaud, Adrien Le Pluart, Paul Arnolfo, Christelle Darrieutort-Laffite

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Théo Renaud, Adrien Le Pluart, Paul Arnolfo, Christelle Darrieutort-Laffite. Pyomyositis of the obturator internus muscle. Joint Bone Spine, 2025, 92 (6), pp.105979. 10.1016/j.jbspin.2025.105979. hal-05390205

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Submitted on 1 Dec 2025

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# Pyomyositis of the obturator internus muscle

Théo Renaud<sup>a</sup>, Adrien Le Pluart<sup>a</sup>, Paul Arnolfo<sup>a</sup>, Christelle Darrieutort-Laffitte<sup>a,b,*</sup>

<figure><img src="image_4.png" /></figure>

<figure><img src="image_5.png" /><figcaption>Fig. 1.</figcaption></figure>

<footnote><sup>a</sup> Service de rhumatologie, CHU Nantes, Nantes, France</footnote>

<footnote><sup>b</sup> Nantes Université, Oniris, CHU Nantes, Inserm, Regenerative Medicine and Skeleton, RMeS, UMR 1229, 44000 Nantes, France</footnote>

<footnote>* Corresponding author at: Department of Rheumatology, CHU Nantes, 1, place Alexis Ricordeau, 44000 Nantes, France. E-mail address: christelle.darrieutort@univ-nantes.fr (C. Darrieutort-Laffitte).</footnote>
Pelvic MRI and CT of a 57-year-old male patient suffering from right hip pain with fever. Symptoms started 5 days before hospital admission. The pain was induced by hip mobilization, especially in internal rotation but without limitation of joint range of motion. The patient had history of prostate adenocarcinoma treated by prostatectomy and radiotherapy 2 years earlier and he was receiving hormonal therapy with Leuproreline acetate. Hip X-rays was normal. Hip ultrasound showed no joint effusion, but CRP level was high (393 mg/l). The magnetic resonance images showed obturator internus muscle edema with hyper intense signal on STIR sequences (red arrows) and hyper intense signal on T1-weighted after gadolinium injection (T1-Gado) (white arrows) (Fig. 1A-B). Pelvic CT images showed a thickening of the muscle (black star) with an abscess (blue arrow) (Fig. 1C). CT-guided puncture of the abscess revealed a *Streptococcus dysgalactiae* leading to the diagnosis

of pyomyositis of the obturator internus muscle. The patient fully recovered after 4 weeks of amoxicillin. The route infection was not identified (no skin wound, negative digestive endoscopy). Pelvic pyomyositis are usually described in children [1,2] and are very rarely reported in adults.

**Disclosure of interest**

The authors declare that they have no competing interest.

**References**

[1] Orlicek SL, Abramson JS, Woods CR, Givner LB. Obturator internus muscle abscess in children. J Pediatr Orthop 2001;21:744-8.

[2] Trusen A, Beissert M, Schultz G, Chittka B, Darge K. Ultrasound and MRI features of pyomyositis in children. Eur Radiol 2003;13:1050-5.