Acute Medicine 2006; 5(1): 13-16 13

Clinical Reviews

Psoas : Diagnosis and Treatment

Dr R Kandasamy, Dr A Srikanth, Dr SM Rutter, Dr CJ Butcher & Dr J Snape

Abstract Psoas abscess is an uncommon presentation on the acute medical take. However recognition and appropriate treatment is essential. This review is designed to highlight the clinical features, microbiology, diagnostic tests and treatment for this condition. In order to illustrate some of the pitfalls and complexities in the management of psoas abscess we have included a case history of a patient who was recently treated in our department.

Keywords Psoas abscess, klebsiella infection, percutaneous drainage, diagnosis, treatment Figure 1. ultrasound scan showing renal abscess. Teaching Points 1. Psoas abscess may be primary or secondary. Computerised Tomography (CT) abdomen 2. Most psoas are secondary and occur confirmed an abscess in the region of the right renal secondary to disease in anatomically related structures. hilum. 3. Psoas abscess caused by klebsiella is often associated As there were no signs of renal obstruction, it with diabetes mellitus and may have a high recurrence was decided to treat conservatively with antibiotics rate. (intravenous Co-amoxiclav). The patient’s 4. Computed tomography (CT) is considered to the gold inflammatory markers improved but she developed a Raj Kandasamy standard investigation for psoas abscess. limp due to pain in the right groin and the MRCP 5. CT guided percutaneous drainage and up to 6 weeks Specialist Registrar of intravenous antibiotics would most commonly be abdominal tenderness and mass persisted. A repeat Geriatric Medicine the treatment of choice for psoas abscess. CT abdomen, after two weeks of treatment on 6. Outpatient parenteral antibiotic therapy may enable antibiotics, showed low attenuation fluid in relation early discharge in patients requiring intravenous Asha Srikanth to right kidney and fluid collection in right psoas MRCP antibiotics. muscle. She developed a right (see Medical SHO discussion). A pigtail catheter was inserted Case report percutaneously under CT control (Figure 2) and 10 SM Rutter MRCP A 71 year old Bangladeshi woman with type 2 ml of thick pus was drained. Escherichia coli, sensitive Consultant Geriatrician diabetes presented with right-sided abdominal pain to coamoxyclav, was grown from culture of the (special interest: of five days duration associated with rigors, dysuria fluid, which was negative for TB. Her intermediate care) and frequency. There was no loss of weight or inflammatory markers normalised and she started appetite and no respiratory symptoms. She had a walking normally. She was continued on antibiotics CJ Butcher previous history of myocardial infarction, atrial for two more weeks, and was then discharged home. FRCR MRCP Consultant Radiologist fibrillation and no history of tuberculosis (TB). Two days later she was readmitted with similar On examination she had temperature of 38.2 C abdominal pain and temperature. There was right J Snape and tenderness in the right upper abdominal upper quadrant tenderness with a prominent right FRCP quadrant with a ballotable mass in right loin. Psoas sign. Investigations showed normocytic Consultant Geriatrician Investigations revealed a normal full blood count and normochromic anaemia with a normal white cell Correspondence: liver function tests but a C- reactive protein (CRP) count and CRP 312. Magnetic resonance imaging J Snape of 153 mg/L. Blood cultures and urine cultures were (MRI) scan confirmed a recurrent psoas abscess King’s Mill Hospital negative and chest x-ray was normal. Abdominal (Figure 3) and no spinal lesion. A CT-guided pigtail Mansfield Road ultrasound showed a 4-5 cm hypo-echoic mass catheter was inserted and 60 mls of thick pus was Sutton in Ashfield adjacent to the right kidney (Figure 1). drained. Notts NG17 4JL Rila Publications Ltd. 14 Acute Medicine 2006; 5(1): 13-16 Psoas Abscess: Diagnosis and Treatment

Both pus and blood culture grew Klebsiella sp., sensitive to Cefuroxime and Gentamicin with which she was treated. Her inflammatory markers improved and the pigtail was removed after three days once CT had confirmed that there was no residual collection. There was a further recurrence when she was changed to oral antibiotics after three weeks and she was treated again with intravenous Gentamicin and Cefuroxime and had a pigtail inserted for the third time. Again 60 ml of thick purulent fluid was drained, which grew Klebsiella and was negative for TB. The drain was removed after three days. Her condition slowly improved and she was discharged home on the Intensive Home Support Scheme (intermediate care) to continue intravenous antibiotics for three weeks (once daily Ceftriaxone and Gentamicin). Figure 2. CT scan with percutaneous drain inserted in the psoas abscess Currently, nine months following discharge, she remains well and has put on 8kg in weight.

Discussion Anatomy Psoas major is a long fusiform muscle which originates from the margins of the 12th thoracic vertebral body and extends through the retroperitoneum to merge with the iliacus muscle (to form the iliopsoas) before insertion on the lesser trochanter of the femur. The psoas muscle lies in close proximity to organs such as the sigmoid colon, , , ureters, abdominal aorta, kidneys, pancreas, spine, and iliac lymph nodes. Hence infections in these organs may spread to the iliopsoas muscle. It is innervated by branches of the 2nd, 3rd and 4th lumbar nerves. The abundant blood supply of the muscle is believed to predispose it to haematogenous spread from occult sites of infection. Iliopsoas abscess may be classified as primary or secondary, depending on the presence or absence of underlying disease. Primary iliopsoas abscess probably occurs as a result of haematogenous spread of an infectious process from an occult source in the body. Primary iliopsoas abscess is more common in patients with diabetes mellitus, renal failure, intravenous drug abuse, AIDS and other forms of immunosuppression.1,2 Most psoas abscesses occur Figure 3. MRI showing right psoas abscess secondary to disease in anatomically related structures (e.g. vertebrae, pancreas, renal tract, ileocaecal junction and secondary abscesses contain enteric organisms.9 Specific aorta). Crohn’s disease is the commonest cause of organisms described in the aetiology of secondary psoas secondary iliopsoas abscess.3,4,5 abscess include clostridium perfringens,10 Yersinia enterocolitica,11 Pasteurella multocida,12 klebsiella Microbiology pneumoniae,3 salmonella typhi,14 methicillin resistant In the early and mid twentieth century mycobacterium Staphylococcus aureus15 and Mycobacterium kansasii.16 tuberculosis (MTB) was the predominant pathogen Psoas abscess caused by klebsiella is uncommon in causing psoas abscess, originating either from direct western communities but is seen more often in the Asian extension from the spine (Pott’s disease) or from population, particularly in Taiwan.13,17 Diabetes mellitus is haematogenous spread from a distant site. As a secondary a common underlying disease in patients infected with cause of psoas abscess, MTB is now uncommon in klebsiella pneumoniae.13,18 It has also been shown that western countries.6,7 patients infected with klebsiella have high recurrence rates Today the most common source of secondary abscess as multiple abscesses may occur and may need is from the bowel (Crohn’s, and colonic percutaneous drainage (PCD) to be performed more than inflammation or neoplasm).3,4,5,8,9 once,13,17 as in our patient. A significantly higher mortality Cultures from a secondary abscess are more frequently has been reported in patients with gas forming klebsiella mixed (56% of 61 cases in one series)9 although 82% of all organisms.

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Poor prognostic indicators include shock, disturbed Some authors believe that magnetic resonance imaging consciousness, high blood glucose and defective immune is superior to computed tomography because of better response,13 particularly in patients with co-existent discrimination of soft tissues and the ability to visualize the diabetes mellitus. abscess wall and the surrounding structures without the In primary psoas abscess, Staphylococcus aureus is the need for intravenous contrast medium.20 Plain abdominal predominant organism, affecting up to 87.5% of cases in radiographs have low diagnostic accuracy, although one large series.9 In the same series streptococcal species occasionally gas forming organisms reveal abscesses as represented 4.9% and Escherichia coli 2.8%. mottled gas shadows in the retroperitoneum.21

Diagnosis Treatment 1. Clinical Features Treatment includes the use of appropriate antibiotics Patients with psoas abscess may present with the and adequate drainage. The choice of antibiotics will be classical triad of fever, abdominal / loin pain and limp, determined by the clinical setting. Patients with likely although this is by no means universal.23 Pain may radiate primary psoas abscesses (e.g. intravenous drug users) to the hip or thigh anteriorly, due to the innervation of the should be started on anti-staphylococcal antibiotics until a muscle by lumbar nerves. Symptoms may also be more specific diagnosis is made. Those with probable secondary non-specific (e.g. malaise and weight loss).23 The abscesses should be commenced on broad spectrum differential diagnosis would include meralgia paraesthetica antibiotics pending a final microbiological diagnosis. due to compression of the lateral femoral cutaneous nerve Drainage of the abscess may be achieved through in the groin – this often causes only paraesthesia. Muscle computed tomography guided percutaneous drainage strain may occur secondary to muscle injury but pain (PCD) or surgical drainage. PCD is much less invasive radiation and systemic symptoms are usually absent. The and has been proposed as the drainage method of choice.25 back pain of sciatica typically radiates to the posterior or In a study of 22 patients of whom 20 patients had primary lateral aspects of the thigh and paraesthesia will usually be and two had secondary iliopsoas abscesses, it was found present in the distribution of the pain. Occasionally that PCD was effective in 21 out of the 22 patients.22 This irritation of the L3 or L4 root can result in back pain which procedure is associated with a low morbidity and radiates to the anterior aspect of the thigh or knee. mortality. However, this is usually associated with paraesthesia and It is said that secondary psoas abscess due to gram the knee reflex will usually be reduced or absent.6 negative organisms are often associated with a large On examination there may be an indication of the collection at presentation (553 mls in one study ),24 source of a secondary psoas abscess (e.g. an abdominal whereas those due to MTB or of primary origin present mass related to a gastrointestinal or genitourinary with a small collection (mean volume 92 mls ).24 Our condition, tenderness over an infected vertebra or signs of patient contradicts this finding. Surgery is indicated if infective endocarditis). Some patients may present with a PCD fails or is contraindicated. The presence of another painless mass below the inguinal ligament which may be intra-abdominal pathology such as Crohn’s disease may mistaken for a femoral or a lymph node. also be an indication for surgery, when a single operation The diagnosis may be clear if the patient has adopted enables drainage of the abscess and resection of the the position which favours the least discomfort, that is diseased bowel.8 Sometimes PCD can be a useful initial supine with the hip slightly externally rotated and the treatment to improve the patient’s condition before knee moderately flexed (so called: ‘psoas sign’).19 surgery. Hyperextension of the hip on the affected side, with the patient lying on the normal side, will result in pain (the Duration of treatment and prognosis ‘reverse psoas’ manoeuvre), as will lifting the ipsilateral Mortality rates of 18-25% have been described in thigh against the examiner’s hand (iliopsoas test).19 These psoas abscess.6,7 The reasons include delayed diagnosis and tests may also be positive in acute appendicitis where there treatment, poor nutritional status, inadequate drainage of is inflammation of the psoas abscess muscle without the abscess and too short a course of antibiotics. abscess formation. There are no guidelines on the duration of antibiotics, but such literature as is available suggests that most Investigations respond to two to three weeks antibiotics after drainage of Laboratory investigations may disclose an elevated the abscess,6,21 but some require up to six weeks of white cell count, ESR or C reactive protein. There may intravenous treatment (as in our case here). The duration be anaemia (often normochromic, normocytic) and blood of treatment will be guided by the subjective response of cultures may reveal the causative organism. the patient and by the response of the acute phase reactants Computed tomography should be performed for a (e.g. WCC and CRP). Outpatient parenteral antibiotic definitive diagnosis and is considered the "gold standard". therapy, as ultimately was used in our case, may enable Ultrasound is inexpensive, has no radiation hazards and is earlier discharge from hospital while continuing with easy to perform but is extremely operator dependant. intravenous treatment. Ultrasound is diagnostic in only 60% of cases.9

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Psoas Abscess: Diagnosis and Treatment

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