Pumice stone sign: Emphysematous osteomyelitis in diabetic ketoacidosis

•Emphysematous osteomyelitis is a rare but fulminant type of osteomyelitis.•'Pumice stone sign' can be seen on plain radiograph.•Diabetes mellitus is a major risk factor.•Poor prognosis, urgent debridement and antibiotics are often required. A 72-year-old female presents with lethargy, fever, and right hip pain for six days. She denies any trauma and had no prior surgical history. Investigations revealed leucocytosis (18.85 × 10^9/L), elevated serum glucose (46.3 mmol/L), ketosis (serum Beta-Hydroxy-butyrate 2.4 mmol/L), and mild acidosis (pH 7.30). Radiographs demonstrates probable intramedullary gaseous lucencies at the right sacroiliac joint (Figure 1). Computed tomography confirmed the presence of gas within the right sacroiliac joint with an extraosseous gas locule along the inferior aspect (Figure 2). These findings were compatible with emphysematous osteomyelitis. Magnetic resonance imaging demonstrated pyomyositis involving the right psoas, iliacus, piriformis, and gluteus maximus (Figure 3A and 3B). Blood cultures yielded Escherichia coli, and the patient recovered uneventfully after six weeks of antibiotic therapy.Figure 2Coronal reformats of the CT pelvis. It confirms the presence of intramedullary gas at the right sacroiliac joint (pumice stone sign) with a small extra-osseous gas locule at the inferior aspect of the joint (circle). No bony erosion is identified.View Large Image Figure ViewerDownload Hi-res image Download (PPT)Figure 3A. MRI of the pelvis. Axial T1-weighted, fat-suppressed, post contrast sequence. There is oedema, increased enhancement and rim-enhancing collections in the right iliacus (arrow), piriformis (curved arrow) and gluteus muscles (arrowhead). These are compatible with pyomyositis. B. MRI of the pelvis. Coronal T1-weighted, fat-suppressed, post contrast sequence. Intramedullary low signal intensities at the right sacroiliac joint (curved arrow), in keeping with emphysematous osteomyelitis. Rim enhancing collection in the right psoas (arrow) and bulky appearance with increased enhancement of the right piriformis (arrowhead), in keeping with pyomyositis.View Large Image Figure ViewerDownload Hi-res image Download (PPT) Emphysematous osteomyelitis (EO) is a rare but fulminant variant of osteomyelitis related to gas-forming organisms. Imaging plays a critical role in early diagnosis. Although "pumice stone sign" is classically described on CT [[1]Ono R Uehara K Kitagawa I. Emphysematous Osteomyelitis of the Spine: A Case Report and Literature Review.Intern Med. 2018; 57 (Jul 15Epub 2018 Mar 9. PMID: 29526940; PMCID: PMC6096010): 2081-2087https://doi.org/10.2169/internalmedicine.0219-17Crossref PubMed Scopus (17) Google Scholar], intraosseous gas can sometimes be identified on plain radiographs [[2]Small JE Chea P Shah N Small KM. Diagnostic Features of Emphysematous Osteomyelitis.Curr Probl Diagn Radiol. 2022; 51 (Jul-AugEpub 2018 Jun 1. PMID: 30042030): 666-672https://doi.org/10.1067/j.cpradiol.2018.05.008Crossref PubMed Scopus (16) Google Scholar]. Diabetes mellitus is a dominant risk factor, and diabetic ketoacidosis may ensue. EO has a poor prognosis with a mortality rate of up to 32% [[3]Luey C Tooley D Briggs S. Emphysematous osteomyelitis: a case report and review of the literature.Int. J. Infect. Dis. 2012; 16: e216-e220https://doi.org/10.1016/j.ijid.2011.11.007Abstract Full Text Full Text PDF PubMed Scopus (51) Google Scholar], and aggressive treatment with surgical debridement and antibiotic therapy is critical. None.