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Rheumatology Advance Access published online on September 26, 2007
Rheumatology, doi:10.1093/rheumatology/kem201
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© The Author 2007. Published by Oxford University Press on behalf of the British Society for Rheumatology. All rights reserved. For Permissions, please email: journals.permissions@oxfordjournals.org

Pyogenic sacroiliitis—a comparison between paediatric and adult patients

M.-S. Wu1, S.-S. Chang1,2, S.-H. Lee3 and C.-C. Lee4,5

1Department of Emergency Medicine, Chang Gung Memorial Hospital, Chang Gung University, College of Medicine, Taipei, 2Department of Nursing, Chang Gung Institute of Technology, Taoyuan, 3Department of Rehabilitation and Physical Medicine, Taipei Veteran General Hospital, Taipei, 4Department of Emergency Medicine, National Taiwan University Hospital, Yun-Lin Branch, Douliu and 5Graduate Institute of Epidemiology, College of Public Health, National Taiwan University Hospital, Taipei, Taiwan.

Correspondence to: Dr C.-C. Lee, Department of Emergency Medicine, National Taiwan University Hospital, Yun-Lin Branch, No. 7, Chun-Shan South Road, Taipei 100, Taiwan. E-mail: chnchnglee{at}ha.mc.ntu.edu.tw


   Abstract
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 Abstract
Introduction
 Methods
 Results
 Discussion
 References
 
Background. Pyogenic sacroiliitis is a rare cause of hip pain and fever. We aim to report a series of 33 patients with pyogenic sacroiliitis and to investigate the differences among paediatric and adult cases.

Methods. Clinical and laboratory data of 33 cases who were admitted to the emergency department with a confirmed discharge diagnosis of pyogenic sacroiliitis between 1996 and 2005 were assessed. All patients were divided into paediatric and adult groups by the age of 15 yr. The features of pyogenic sacroiliitis and clinical outcome were compared among the two groups. Several factors were analysed including gender, age, clinical signs and symptoms, laboratory tests, radiological examinations and scintigraphy.

Results. Among the all included patients, females were attacked more frequently than males (3: 1). One-third of patients had concurrent infections, of which urinary tract infections were the most common (41.6%). Compared with adult patients, paediatric patients tend to have fewer comorbid immunocompromized conditions, fewer concurrent infections, more equality in gender distribution and more presentations of weight bearing difficulty. Staphylococcus aureus was the main blood culture isolate from paediatric patients (80%), but only accounted for half of those from adult patients. Group B streptococcus and Salmonella spp. were not uncommon in the adult patients. Scintigraphic bone scan has the highest sensitivity (93.3%) and remains the image modality of choice. When local abscess formation is suspected, computed tomography or magnetic resonance imaging may be the preferred method used for examination.

Conclusion. This case series should alert the physicians to the possibility of pyogenic sacroiliitis and the difference between paediatric and adult patients.

KEY WORDS: Pyogenic sacroiliitis, Scintigraphic bone scan, MRI, Infectious arthritis


   Introduction
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 Abstract
 Introduction
Methods
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Pyogenic sacroiliitis is relatively rare, representing only 1–2% of all cases of septic arthritis [1]. Initial symptoms are usually non-specific and difficult to differentiate from sciatica or septic arthritis of hip, and sometimes may mimic acute abdomen and sepsis syndrome [2]. Low awareness of the clinical presentation and lack of knowledge of the diagnostic procedure usually lead to delay in diagnosis. Delay in diagnosis may lead to several severe complications such as abscess or sequestrum formation, prolonged period of sepsis, long-term joint deformity and disability and even death [2, 3]. Until now, fewer than 200 confirmed cases have been reported in the English literature [4]. This study will characterize a series of 33 patients diagnosed with pyogenic sacroiliitis who were admitted to the emergency department (ED) of a university hospital over a 10-yr period. We also compared the clinical manifestations between two different age groups: child and adult. Better understanding of the clinical profile in each age group may lead to the development of diagnostic protocols.


   Methods
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The hospital records of all ED patients diagnosed with pyogenic sacroiliitis between 1996 and 2005 were reviewed by the study physicians through a computerized search by ICD-9 code of 711.05 (pyogenic arthritis involving pelvic region and thigh), 711.0 (pyogenic arthritis) and 720.2 (sacroiliitis, not elsewhere classified). The diagnosis of pyogenic sacroiliitis was confirmed by the presence of characteristic history, physical findings of hip pain or low back pain and definite radiological evidence on scintigraphic bone scan, pelvic computed tomography (CT) or magnetic resonance imaging (MRI). Radionuclide scintigraphic scans include gallium-67 and technetium-99m methylene diphosphonate (Tc99m-MDP) bone scan. The availability of the three imaging modalities did not vary over the study period. Bone scan was available during the day time, while MRI and CT were available at any time. Patients with underlying autoimmune spondyloarthropathy and lacking in strong evidence for bacterial infection (i.e. positive blood culture, positive synovial fluid culture or local abscess formation) were excluded for analysis.

All patients were divided into two age groups for analysis. The defining ranges of age for two groups were less than or equal to 15 yr and greater than or equal to 16 yr. We analysed the mean age, gender composition, clinical signs and symptoms, and results of laboratory tests in each age group. Fever was defined as the highest controlled tympanic temperature >38.3°C and leucocytosis was defined as leucocyte count ≥12 000 cells/mm3. We followed the outcome and related complications of all patients for at least 1 yr by medical records of hospital treatment course and follow-up clinics. Related complications include residual low back pain, psoas muscle abscess or septic syndrome [5–7]. Data analysis was performed by using SPSS software for Windows (Version 13.0; SPSS, Inc., Chicago, IL, USA). Descriptive statistics were performed by calculating the mean and S.D. for continuous variables. Absolute and relative frequencies were calculated for categorical variables. Group comparisons were using Chi-square or Fisher exact tests, as appropriate. All tests were two-tailed and P-values <0.05 were as considered statistically significant. The study protocol was approved by the institutional review board and the ethic committee of the university hospital.


   Results
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 Introduction
 Methods
 Results
Discussion
 References
 
A total of 33 patients were identified and included in the study. There were 11 (33.3%) paediatric patients and 22 (66.7%) adult patients. Mean age of the 33 patients was 36.9 ± 24.5 yr (range 3–80 yr). Fifteen (45.5%) patients had predisposing conditions, including recent pelvic trauma, recent spinal surgery or an overt evidence of concurrent infection elsewhere. Mean length of hospitalization was 24.6 days (range 7–113 days). One patient (3%) died of severe sepsis and multiple organ failure. The demographic features and clinical manifestations in the two different age groups are summarized in Table 1. Gender distribution was roughly equal in the paediatric group, but tended to be female predominant in the adult group (45 vs 63%). The trend is even more prominent in elderly patients. Six of the eight patients (75%) older than 60 yr are females. Right side sacroiliac joints were found to be slightly more frequently affected than left side or bilateral involvement in both age groups, although statistical significance was not attained. The adult patients were more likely to present atypically. Only 14 adult patients (63.6%) in contrast to nine paediatric patients (81.8%) presented with the full clinical triad of fever, low back pain and difficulty in weight bearing. Leucocyte count was not a sensitive laboratory marker in detecting pyogenic sacroiliitis in this cohort: only 45.5% had elevated leucocyte counts. C-reactive protein (CRP), however, was a more sensitive marker. Among the 26 patients (78.7%) whose serum CRP concentrations were measured, 19 (73.1%) patients had a serum CRP concentration >60 mg/l. Mean concentrations of CRP were 149 ± 111 mg/l. There was no statistical difference in the proportion of CRP elevation between the paediatric and adult patients (70 vs 75%, P = 0.78).


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  		TABLE 1. Clinical manifestations of 33 patients with pyogenic sacroiliitis

 
A total of 45% of adult patients had concurrent infectious diseases. Urinary tract infection was the most common concurrent infection, especially in the adult group. Blood cultures were performed in all of these 33 patients and 19 patients grew organisms. The overall positive blood culture rate was low (57.6%), especially in the paediatric group (45.5%). Synovial fluid culture, however, had a higher positive culture rate. Twelve patients (36%) underwent synovial fluid aspiration because of abscess formation found on CT or on MRI, and nine patients (75%) yielded growth of organisms in synovial aspirates. The most common bacterial pathogen recovered from blood and/or the synovial fluid specimen was Staphylococcus aureus, accounting for 80% of blood culture isolates in paediatric patients and 50% in adults ones. The culture results of adult patients had a wider spectrum of bacteriology. Group B streptococcus and Salmonella spp. were cultured in three and two patients, respectively. Table 2 summarized the concurrent infections and blood culture results in the two groups of patients.


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  		TABLE 2. Source of concurrent infection and blood culture results

 
Table 3 summarized the diagnostic imaging modalities and positive rates in the two age groups. The overall imaging positive rates for X-ray, CT, MRI and bone scan were 12.1, 36.4, 84.6 and 93.3%, respectively. Pelvic X-ray was routinely performed in 33 patients, but had a low sensitivity in detecting pyogenic sacroiliitis. Only four cases revealed sclerotic change of sacroiliac joints. Eleven patients received abdominal or spinal CT examinations. The decision of CT exams was based on the clinical diagnosis of sepsis syndrome originated from abdomen or paraspinal area by primary care physicians. Only 4 (36.4%) of the 11 cases had positive finding on CT examination, all of which were elderly patients who were aged more than 60 yr. Thirteen patients received MRI examination because spinal cord compression was suspected by the clinicians. Of the 13 patients, 11 (84.62%) patients revealed abnormal focal signal intensities representing inflammatory reaction or abscess formation. Bone scan was arranged in 31 (93.9%) patients with clinical suspicion of pyogenic sacroiliitis. Two patients did not receive bone scan exam because the diagnosis had been clearly shown on CT or MRI. Tc-99m MDP bone scan was prescribed at first, followed by gallium-67 bone scan if necessary. As shown in Table 3, more than 93% of these bone scan examinations revealed characteristic changes. Representative radiological images of bone scan, MRI, and CT images are shown in Figs 1–3GoGo.


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  		TABLE 3. Comparison of results between conventional radiography (X-ray), CT, MRI and scintigraphy examination

 

Figure 1
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  		FIG. 1. Tc-99m MDP bone scan scintigraphy performed 28 days after onset of patient's symptoms reveals increased uptake of radioactivity involving bilateral sacroiliac joints. The uptake ratio of right sacroiliac joint is much higher than left one. Pyogenic sacroiliitis was highly suspected (arrows).

 

Figure 2
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  		FIG. 2. (A) Axial T2-weighted image taken 12 days after onset of the patient's symptoms shows abnormal enhancement in the left sacroiliac joint (arrow) and multiple small cystic spaces with enhancement in posterior paraspinal soft tissue and left iliopsoas muscle, suggesting abscess formation. (B) Coronal T1-weighted image shows destruction of the left sacroiliac joint with abnormal enhancement suggesting sacroiliitis (arrow).

 

Figure 3
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  		FIG. 3. Computed tomography taken 2 weeks after onset of the patient's symptoms shows infectious process at right sacroiliac joint with cortex destruction (black arrow) and perifocal abscess formation (white arrow).

 
All patients were treated for 2–6 weeks with intravenous antibiotics followed by oral antibiotics for 2–3 weeks. Surgical debridement was performed in only 3 of 33 patients (9.1%) due to multiple abscess formation and/or poor response to antibiotics treatment. Twelve patients (36.4%) had chronic musculoskeletal sequelae, including chronic hip pain in five, gait abnormality in four, lower extremities weakness in one and radiculopathy in one patient. The proportion of patients with chronic complications was not different in paediatric and adult patients (36.4 vs 36.4%, P = 1). There was one patient who died of methicillin-resistant S. aureus (MRSA) sepsis and multiple organ failure.


   Discussion
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 Abstract
 Introduction
 Methods
 Results
 Discussion
References
 
In this study we found that pyogenic sacroiliitis occurred in patients of all ages. Female patients tend to have a higher incidence than do male patients, especially in the elderly patients. Previous series of pyogenic sacroiliitis showed male predominance, however, they did not analyse on the gender difference among different age groups [8]. We found that in the adult group, especially in the elderly subgroup, females may be at higher risk for developing pyogenic sacroiliitis. Whether this is due to the race difference or other undetermined factors remains to be answered.

It has been reported that the varied presentation of symptoms and signs of pyogenic sacroiliitis was always remote from the site of infection [9]. In the study cohort, only 14 adult patients (63.6%) in contrast to 9 paediatric patients (81.8%) presented with the full clinical symptoms classical for pyogenic sacroiliitis and only 15 (45.5%) patients had elevated leucocyte counts. We therefore suggest that physicians should keep a high index of suspicion and arrange CRP evaluation for adult patients with atypical presentations. Although previous studies showed that almost all cases of pyogenic sacroiliitis were unilateral, and somewhat more frequently in the left side, these series were mostly paediatric patients [3, 10]. In our series, right sacroiliac joint is more frequently involved than left side in both age groups, and bilateral involvement is not uncommon. Such difference may be due to the relative few paediatric cases in this series, but we could not exclude the possibility of selection bias in either present or previous series such as difference between inclusion criteria.

In accordance with previous series, our series found that the blood culture yield rate was low. However, local synovial fluid cultures had a high yield rate for pathogens. Synovial fluid aspiration was not universally performed in our patients because sacroiliac joint synovial fluid aspiration is technically difficult. In some patients of our series, several attempts failed to obtain synovial fluid in spite of echo- or CT-guidance. We had three patients with dry tapping of the sacroiliac joints synovial fluid aspiration. To overcome this problem, previous literature suggested that 3–4 ml of sterile 0.9% normal saline injection may improve the positive culture rate under the circumstances of dry tapping [11]. In accordance with the previous reports, the leading bacterial pathogen in our series was also S. aureus [2, 12, 13]. Therefore, anti-staphylococcal agents such as oxacillin should be the drug of choice for empirical therapy [14, 15]. However, some highly resistant Gram-negative strains such as Acinetobacter baumannii, Citrobacter freundii or Salmonella enterica serovar Enteritidis were noted in our series, especially in adult patients. The clinicians therefore, should think of the possibility, and prescribe antimicrobials with coverage of Gram-negative pathogens in patients with poor response to initial empirical anti-staphylococcal therapy. In addition, community acquired MRSA has become an emerging threat in our series. We found one 54-yr-old male patient who died of MRSA sepsis and another 56-yr-old female patient who had prolonged admission course (113 days) due to the delayed diagnosis of MRSA infection. These conditions signify the fact that MRSA is emerging as a growing threat even though the patients come from the community.

With the benefit of ease of performance, low cost and low radiation exposure coupled with the high accuracy, radionuclide scintigraphic bone scan has long been viewed by most radiologists as the primary method for the evaluation of pyoarthritis of sacroiliac joints [16–18]. Besides, scintigraphic bone scan also can detect other infective foci existing in the body simultaneously. It also has been suggested that the performance of sequential scintigraphic technetium and gallium scan could increase the specificity of this test [19]. Recently, there are some different viewpoints suggesting that MRI is superior to scintigraphy or conventional radiography in the assessment of active change in the sacroiliac joint [20, 21]. In our patients, both scintigraphic bone scan and MRI study showed high sensitivity in detecting pyogenic sacroiliitis, but MRI has the advantage of characterization of the local abscess formation with/without spinal involvement, which is important in the decision of surgical intervention. In our series, CT has low sensitivity in detecting pyogenic sacroiliitis. Only 4 of 10 (40%) adult patients showed positive findings. Because CT is sensitive in detecting cortical bone destruction, we suggest that elderly patients with inherent osteoporosis, may be more prone to develop cortical bone destruction early in the course of pyogenic sacroiliitis and thus may be more suitable to choose this imaging modality.

We acknowledge that there are some limitations to this study. First, this study was retrospective in design and thus suffered from the inherent bias associated with any retrospective studies. Second, although our series comprising 33 patients was relatively large case number as compared with previous series, statistically, the case number in two age groups was still not large enough for meaningful comparisons in many clinical parameters. Besides, since this is a single centre data analysis, we cannot exclude the possibility of selection bias inherent in this design. But due to the rarity of this disease and the significant clinical consequence if not diagnosed early, we thought a case series study of this kind may still offer some clinical perspective for the clinicians. Thus, it is necessary in the future to identify the difference between races and to promote a more optimal diagnostic and treatment protocol about pyogenic sacroiliitis. It is our belief that the clinical presentation described in this case series should alert the physicians to the possibility of pyogenic sacroiliitis in suspected patients, with the consideration of the substantial difference in clinical manifestations between paediatric and adult patients.

Formula

The authors have declared no conflicts of interest.


   References
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 Abstract
 Introduction
 Methods
 Results
 Discussion
 References
 

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Submitted 2 April 2007; revised version accepted 18 June 2007.
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Comment on: Pyogenic sacroiliitis--a comparison between paediatric and adult patients
Rheumatology, May 1, 2008; 47(5): 740 - 741.
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