The Triad of Psoas Abscess: An uncommon Onset and Elusive Diagnosis

Abstract

Turkish Abstract

Introduction

Psoas muscle abscess is a pyogenic inflammation of iliopsoas muscle. It may be secondary to septicemia or another disease process around the iliopsoas muscle ¹. It is a rare clinical condition with high mortality and morbidity. Although it has nonspecific clinical symptoms and signs, increased use of abdominal computerized tomography (CT) or magnetic resonance imaging (MRI) to evaluate septic patients with unknown foci makes the diagnosis easier.

Psoas abscess (PA) may be classified as primary or secondary depending on the etiology of infection ². Primary PA occurs as a result of haematogenous spread of an infection from an occult source especially in young adults. It may be presented in patients with diabetes mellitus, intravenous drug abuse, AIDS, renal failure and  immunosuppresion ². The classical clinical triad is fever, back pain and limp pain, seen in only 30% of the patients. Abdominal pain, malaise, nausea, and weight loss are the other symptoms ³. Secondary causes are  direct spread of the infection  from adjacent structures, most commonly  seen in Crohn?s disease or any surgical or instrumentation of adjacent anatomical structures, seen in elderly  patients ⁴.

Treatment of PA with antibiotherapy alone is not commonly reported in the literature. Open or percutaneous drainage plus antibiotheraphy are the most effective treatment method for PA ^4-6. As open drainage method may be associated with significant morbidity in the septic patients, the less invasive drainage methods  such as percutaneous catheter drainage under radiological guidance has become the preferred treatment method.

We report a 89-year-old male who was admitted with limp and back pain. Psoas abscess was detected on MRI, and treated with antibiotherapy plus percutaneous drainage with the insertion of an ultrasound-guided pigtail catheter.

Case Report

A 89-year-old male patient was presented to the Emergency Department (ED) with limp and back pain. He was admitted to hospital three weeks ago because of urinary tract infection. The patient had a history of type II diabetes, Alzheimer?s disease, hypertension, congestive heart failure and benign prostatic hyperplasia. He had no history of tuberculosis. His vital signs were stable. Physical examination was within normal limits. Laboratory studies demonstrated no abnormal values except mildly elevated creatinine level as 1.3 mg/dL. WBC count was 7.900 K/uL. Non-contrast enhanced CT scan of the lumbar spine was obtained and revealed normal spinal cord and vertebral column. Patient?s symptoms improved  and he was discharged from ED. The following day, he presented to ED again with the same complaints. He was referred to orthopedic surgery because of ongoing pain and an urgent lumbar spine MRI scan was performed. MRI scan demonstrated multiple psoas abscesses - the biggest was 4.5x7.7 cms- on both sides and left sided iliopsoas bursitis (Figure1 and Figure2).

Figure 1 There is no evidence of any psoas abscess except the asymmetry in the size of psoas muscles (red arrow).

Figure 2 A large hyperintense psoas abscess is demonstrated in the right psoas muscle on MRI image (T2 ) (red arrow) and multiple small abscesses in the left psoas (blue arrow).

Percutaneous drainage was performed with the insertion of an ultrasound-guided pigtail catheter and patient was admitted to infectious disease ward. The patient was treated with intravenous antibiotics. A pus culture showed a mono-organism -Escherichia coli (E. coli) and Enterococcus was isolated from blood culture in the patient. Blood, urine and pus cultures were negative for ARB.  He was discharged after 51 days without any complications.

Discussion

Pyogenic PA may be divided into two groups according to its etiology. Primary PA occurs due to hematogenous or lymphatic spread of etiologic agent from a distant site, and secondary  PA occurs from an adjacent infectious or inflammatory process by direct expansion ⁴. The leading infectious agents  in patients with PA are  methicillin-susceptible Staphylococcus aureus (27%), and Escherichia coli (18%) ⁷. Primary PA is most probably secondary to an unrecognized staphylococcic infection, ⁸ however,  secondary PA is generally caused by enteric pathogens that arise from intraabdominal region, particularly intestinal origin ^2,4,9,10. Urinary tract infection and instrumentation of the renal region may be an origin for secondary PA ^4,7,11,12. As the etiologic agents in our patient were Escherichia coli and Enterococcus, and the history of urinary tract infection was positive three weeks ago, he was evaluated as secondary PA.  Other causes of secondary PA such as Crohn?s disease, appendicitis, ulcerative colitis, diverticulitis, colorectal carcinoma, hepatocellular carcinoma, spinal tuberculosis, infectious sacroiliitis, endocarditis, instrumentation or catheterization of renal tract and/or femoral artery were not present in our patient.

The initial diagnosis of PA,  based on an accurate history and comprehensive physical examination,  must be  made with the raised suspicion of PA.  History should include the progression of symptoms as well as contributing factors such as gastrointestinal, urogenital, and musculoskeletal disorders ⁴. The classic triad of PA may only be present in 1/3 of cases ³. Nonspecific symptoms such as low-grade fever and malaise may progress into more specific symptoms like abdominal/flank discomfort, pain on movement of the hip secondary to irritation of the muscle belly, externally rotated and flexed hip, referred pain from the nerve roots L2-L4, which supply the psoas muscle ^13,14. Appropriate diagnostic modalities for PA include laboratory (i.e. full blood count, C-reactive protein, erythrocyte sedimentation rate, blood cultures) and radiologic investigations (i.e. ultrasound, CT scan, MRI). Laboratory studies of  pus and blood cultures were diagnostic in our patient. One of the common causes of PA in developing countries is spinal tuberculosis-Pott?s disease, which should be ruled out in all patients. Our patient showed negative culture results of ARB.

MRI has many advantages than CT because of better discrimination of soft tissues and ability to visualize the abscess wall and the surrounding structures ^15,16. The PA in our patient was detected on MRI. Abscesses with low attenuation and no air-fluid presentation cannot be determinated  by CT scan and also non-contrast enhanced CT scan modalities are inappropriate for detecting abcesses  as seen in our patient. Zissin et al. reported that even though non-classical presentations were present, the CT scan was an effective imaging modality for diagnosing PA. The present series proves the importance of the diagnostic and therapeutic role of CT scans ¹⁷.

An ultrasound-guided percutaneous drainage by pigtail catheter is possible for diagnosis and treatment as performed in our patient. The major limitation of ultrasound-guided percutaneous drainage is its technical difficulties to drain  abscesses with multiple separations, small abscesses, and abscesses located in unreachable sites ^6,18,19. Many small abscesses may be treated with antibiotics alone ²⁰. The possible therapeutic approach of abscesses which do require drainage may be aspiration via CT guidance and antibiotic therapy ^4,5.

In secondary PA,  it is wise to start broad spectrum antibiotic treatment that covers S.aureus and also gram negative and anaerobic bacteria ^{2,4,5,14,18-20}. Some authors believe that targeted antibiotherapy alone will sufficiently treat abscesses up to 6 cm diameter ²⁰. Although,  the majority of PA may be aspirated effectively by CT guided percutaneous drainage, ⁵surgical drainage may be preferred in some conditions ⁴. In patients with intra-abdominal pathology such as complex Crohn?s disease or diverticulitis and also failure of the CT guided percutaneous drainage,  surgery is indicated ^14,19-21.

Psoas abscess is a rare disease. The clinical presentation of psoas abscess is often variable and non-specific. Emergency physicians should always be alert about the situations such as prolonged fever of unknown origin, back pain, and/or limp pain. Percutaneous drainage remains the primary initial treatment modality for psoas abscess. Surgical drainage may be preferred, if necessary. Early management and drainage of the abscess reduce  the morbidity and mortality.

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