A thirty-one-year-old woman (gravida 4, para 4) presented to our emergency department with symptoms of fever and pain in the right buttock for three days. The pain had begun two hours after a normal vaginal delivery. The past medical history noted sclerotherapy for varicose veins on both lower extremities two years earlier. The patient denied any recent history of intramuscular drug injection. Vital signs included a temperature of 38.8°C and a pulse rate of 99. On physical examination, there was limitation of right hip motion and a positive test for flexion, abduction, and external rotation (FABER). The right leg had normal muscle strength, with no swelling, warmth, or erythema.
Laboratory studies, including complete blood-cell count as well as kidney and liver function tests, were normal except for leukocytosis (white blood-cell count: 14 × 109/L; lymphocytes: 9%; neutrophils: 84%), an elevated C-reactive protein level of 132 mg/L (normal, less than 5 mg/L), and an elevated erythrocyte sedimentation rate of 110 mm/h (normal, 0 to 15 mm/h). The urinalysis and the subsequent urine culture specimen were negative. The rose bengal test for Brucella was also negative.
The patient was admitted to the hospital with a diagnosis of postpartum pyrexia and was administered ceftriaxone (1 gm intravenously twice daily), metronidazole (500 mg intravenously three times a day), diclofenac sodium (75 mg intramuscularly twice daily) to relieve pain, and omeprazole (20 mg orally once daily).
The next day, the patient became afebrile but still had right buttock pain. Pelvic radiographs showed sclerosis of the right sacroiliac joint. Since this sclerosis was more evident in the iliac portion, it was suggestive of osteitis condensans ilii (Fig. 1). However, because the clinical findings and the positive FABER test favored septic sacroiliitis, pelvic magnetic resonance imaging (MRI) was performed, and T2-weighted and short tau inversion recovery (STIR) images revealed widening of the right sacroiliac joint with joint effusion, sclerosis, and adjacent bone marrow edema with bulging of the anterior joint capsule and inflammation (Fig. 2). The T1-weighted images showed sclerosis (Fig. 3-A) surrounded by intermediate signal, which was evident after contrast (gadoversetamide injection) enhancement (Fig. 3-B). There was abnormal enhancement of the soft tissues anterior and posterior to the right sacroiliac joint. These findings were consistent with septic sacroiliitis. Therefore, aspiration by guided computed tomography (CT) was performed on the fourth day after admission, and 3 mL of joint aspirate was obtained and sent for culture.
On day six, the antibiotics were changed to piperacillin/tazobactam (4.5 g intravenously every six hours) for broader coverage of gram-negative bacterial infections. On the same day, the results of the aspirate culture came back positive for Enterobacter species. This species was sensitive to amikacin, cefepime, gentamicin, imipenem, ciprofloxacin, and ertapenem, and was resistant to cefotaxime, cefoxitine, ceftriaxone, and ceftazidime by the disk diffusion method. On day ten, the antibiotic was changed to ertapenem (1 g intravenously once daily). This delay in antibiotic switch occurred because the infectious disease team was not informed of the culture result until day ten.
On day thirteen, the patient noted that the pain was substantially reduced. The white blood-cell count was within the normal range. The erythrocyte sedimentation rate and C-reactive protein level showed progressive improvement. The patient was discharged on ertapenem therapy (1 g intravenously once daily for four weeks), followed by imipenem therapy (500 mg intravenously every six hours for another month) since ertapenem was no longer obtainable because of insurance issues. However, because she continued to have occasional mild-to-moderate pain, treatment was continued with ciprofloxacin (500 mg orally twice daily) for another two months until the pain had almost completely resolved.
At the ten-month follow-up, the patient was doing very well. An MRI showed complete resolution of the sacroiliitis (Fig. 4), and the inflammatory markers were normal.
This case documents the diagnosis of postpartum pyogenic sacroiliitis caused by the Enterobacter species. The patient presented shortly after delivery with fever and right buttock pain. An MRI showed sacroiliitis of the right sacroiliac joint, and the joint aspirate specimen grew the causative pathogen. The patient was treated with two months of parenteral antibiotics followed by another two months of suppressive oral therapy, and she had a successful outcome.
A review of the English-language literature revealed twelve reported cases of postpartum sacroiliitis: five of these cases had no obvious risk factors and could be classified as primary (Table I), while the other seven cases were secondary to various underlying causes (Table II). In our patient, no obvious risk factor other than pregnancy was present.
Pyogenic sacroiliitis is uncommon and usually related to trauma, illicit drug use, and gynecological infections1-3. The etiology is generally hematogenous since this condition is more frequent in intravenous drug abusers and those with recent infection elsewhere4-6. Several organisms have been reported to cause this problem, with Staphylococcus aureus being the most common3-5,7. To the best of our knowledge, ours is the first case report that describes Enterobacter as an etiology in postpartum pyogenic sacroiliitis. The Enterobacter could have originated from the gastrointestinal or the genitourinary tract during or immediately following the delivery, or perhaps from a venous access as part of hospital-acquired bacteremia. Hence, it is difficult to discern which one of these sites represented the actual contributing source. The possibility that the Enterobacter was a contaminant is excluded since the aspiration was performed under aseptic technique and the growth occurred after seventy-two hours of incubation.
Pyogenic sacroiliitis has a predilection for the iliac side of the sacroiliac joint as a result of the protection afforded by the increased thickness of cartilage on the sacral side8. Pregnant and postpartum women are at particular risk because of microscopic damage to the pelvic joints and ligaments that occurs during delivery2,9. In the literature, all cases of postpartum septic sacroiliitis involved one side, except for two cases that showed bilateral involvement1,10. Of note, the left side was involved in most of the primary cases9-11; even in the single report that described bilateral involvement from that group, the pain had initially started on the left side1. In contrast, our patient had right-side involvement. We believe this to be a rare finding since involvement of only the right side has been described once in the primary cases shown in Table I. We cannot explain this predilection for the left side, and it is possible that it is a false observation because of the small sample size.
In the cases that have been previously reported, the diagnosis was delayed with a minimal delay of eleven days. This is primarily because this is a rare condition and there is a wide differential diagnosis for hip pain in pregnancy-related conditions. Because of the high index of suspicion and the use of MRI, we were able to make the diagnosis in our patient at two days following admission.
Imaging studies have an essential role in the diagnosis of septic arthritis; bone scintigraphy is a sensitive indicator of inflammation, and increased uptake may occur within forty-eight to seventy-two hours from the onset of symptoms. However, the test is not specific, particularly in postpartum patients because of the stress on the pelvic joint during delivery1-3. The imaging study of choice in the early diagnosis of septic arthritis in the sacroiliac area is MRI; findings include joint effusion, bone edema, and soft-tissue fluid collection. The test should include a combination of axial and coronal spin-echo sequences, T1-weighted sequences (with and without contrast), T2-weighted sequences, and STIR sequences8. CT-guided aspiration, when possible, is also advised in order to identify the causative organism1,2.
Parenteral antibiotics for four to six weeks similar to those administered for non-postpartum pyogenic sacroiliitis are usually recommended4. In addition, oral suppressive antibiotics should be used once the patient’s clinical condition is stabilized2. Furthermore, the erythrocyte sedimentation rate and C-reactive protein level could be used to assess the response to treatment2. Our patient continued to have mild-to-moderate pain after finishing two months of the parenteral antibiotic therapy. Therefore, we continued treatment with oral therapy until the symptoms had complete resolution.
Although it is difficult to eliminate the possibility of future recurrence since the follow-up period was only ten months, we believe this possibility is unlikely because the patient was treated promptly, had complete resolution of symptoms, and the imaging showed marked improvement.
In conclusion, pyogenic sacroiliitis should be included in the differential diagnosis of postpartum patients with fever and hip pain. Successful treatment can be achieved by early diagnosis with the use of MRI, joint aspiration, and prolonged pathogen-directed antibiotic therapy.
Disclosure: None of the authors received payments or services, either directly or indirectly (i.e., via his or her institution), from a third party in support of any aspect of this work. None of the authors, or their institution(s), have had any financial relationship, in the thirty-six months prior to submission of this work, with any entity in the biomedical arena that could be perceived to influence or have the potential to influence what is written in this work. Also, no author has had any other relationships, or has engaged in any other activities, that could be perceived to influence or have the potential to influence what is written in this work. The complete Disclosures of Potential Conflicts of Interest submitted by authors are always provided with the online version of the article.