Psoas abscesses are an uncommon occurrence1
and may be primary or secondary based on the presence or absence of an underlying aetiology. Nowadays, primary psoas abscesses are often due to haematogenous spread of an infection process from an occult source especially in immunocompromised and elderly patients.2
The most common pathogens are Staphylococcus aureus
(88.4% of cases), streptococci (5%) and Escherichia coli
Poor nutrition and low socioeconomic class are regarded as risk factors. Secondary psoas abscesses are classified as those which occur by direct spread from contiguous structures. Previous reviews have shown worldwide variations in the aetiology of this disease.1 4 5
Several diseases have been implicated with Crohn's disease being the most common (60%) and other causes being appendicitis (16%), ulcerative colitis, diverticulitis, colon cancer (together 11%) and VO (10%).4
Secondary psoas abscesses are caused mainly by E coli
species.4 Mycobacterium tuberculosis
as a cause of psoas abscesses is currently rare in the USA but, in areas of the world where tuberculosis is still a common disease, it continues to be an important pathogen.6
Unusual causes are not uncommon, and there have been case reports of psoas abscesses secondary to My kansasii6
and M xenopi
Locally, there has been a report of a bilateral case of this disease attributed to disseminated granuloma inguinale.8
Psoas abscesses may present with vague and often non-specific symptoms. A high index of suspicion is mandatory to enable early recognition of this rare clinical disease. The classical clinical trial consisting of fever, back pain and limp is present in only 30% of cases.9
This was quite typical in our case, which was further supported by the examination findings.
With the increasing use of ultrasonography and CT, cases of psoas abscess are being diagnosed earlier and more frequently; thereby, decreasing the morbidity and mortality of this illness.10 11
CT better evaluates the retroperitoneal areas identifying additional collections, which may require separate drainage if percutaneous drainage is utilised.
Treatment involves the use of appropriate antibiotics as well as drainage of the abscess.3
Knowledge of common pathogens should guide initial choice of antibiotics. Some authors advocate a surgical approach—in particular if the CT demonstrates involvement of adjacent structures.12
Several studies have substantiated the effectiveness and relative safety of percutaneous drainage of abdominal abscess.13
Benefits include avoidance of general anaesthesia and laparotomy as well as prolonged postoperative admission to hospital. Although our patient spent an extended length of time in hospital, this was attributed to his comorbid illnesses and the concurrent finding and treatment of his VO. Our patient had drains removed after 4 weeks as he had clinically significant drainage from the sites until then, and it has been recommended that abscess drainage needs to be continued until obliteration of the abscess cavity occurs and there is evidence of clinical improvement.14
Successful treatment generally requires long term (2–4 weeks) drainage and this was assessed by sequential sonography, clinical examination, measurements and observations of the drainage.
Recurrences usually indicate an underlying uncorrected problem. The treatment protocol in our patient was quite successful as there was no recurrence. The presence of VO extended his treatment regimen and he had 8 weeks of dual antibiotic treatment. VO is usually caused by S aureus
and coagulase-negative staphylococci.15
Anaerobic infections are much less implicated in spine and disc space infections, and Bacteroides
account for only about 8% of isolates from bony infections. A report in 2007 has reviewed 12 cases of VO secondary to Bacteroides,
and diabetes mellitus, Gaucher's disease, SCD and rheumatoid arthritis have been indicated as possible predisposing factors. Even though it is an uncommon cause of VO, its presence should be considered in those who have contiguous intra-abdominal or pelvic infections or who have had recent gastrointestinal procedures that may lead to Bacteroides
bacteraemia. Out of the 12 cases cited, 9 were shown to have documented elevated ESR and CRP levels as has been shown in the present case as well. Positive blood cultures were seen in only 33% of the cases. Even though metronidazole is the drug of choice for managing Bacteroides
infections, and there is no data supporting the use of dual antibiotic treatment, this regime has been used in the past with psoas abscess in an immunocompromised patient.16
As our patient was also immunocompromised from the presence of SCD as well as having had a splenectomy, both clindamycin and metronidazole were used. An extended period of intravenous treatment was used as it has been recommended that antibiotic treatment be individualised,14
and a falling ESR has been used as a marker of improvement.17
We used both a fall in ESR and CRP as inflammatory markers, along with clinical improvement, to guide our management.
Despite that fact that SCD causes much reduction in host immune responses, psoas abscesses have been only rarely reported in this population. Psoas abscesses as a result of VO have been even less frequently described with the only case being found in the literature presenting with Salmonella
species continue to be the most prevalent causative organisms causing osteomyelitis in patients with SCD, anaerobic causes are relatively uncommon.19
Patients who have SCD may be more susceptible to acute anaerobic osteomyelitis due to focal gut mucosal ischaemia, translocation of bacteria and seeding in infarcted bone marrow.20
Although believed to be rare, it is likely that VO is underdiagnosed. Septic involvement of the spine may cause collapse,21
may cause fusion of vertebral bodies22
and may present as psoas abscesses. Patients with SCD and bone pain present a diagnostic dilemma between avascular bony crises and osteomyelitis, and a high index of suspicion is required to help make a clear diagnosis.
- SCD will compromise host immune responses; worse in cases that have had a splenectomy.
- Although back pain is a common site for painful crises in those with SCD, other causes, such as VO and psoas infections, should be considered in them as well.
- Salmonella species are commonly associated with osteomyelitis seen in SCD, but more uncommon organisms may be a cause.