(P96) A Case of a Psoas Abscess Complicated by Septic Arthritis Secondary to an Enlarged Communicating Iliopsoas Bursa: An Unusual Lethal Cause of Unilateral Lower Extremity Pitting Edema

Chief Complaint : Left hip pain and left leg swelling

History of Present Illness : A 76-year-old female presented to the emergency department for one month of worsening left hip pain and one week of left leg swelling involving the entire left lower extremity. Her medical history is significant for multiple myeloma with remote bone marrow transplant, osteoporosis, hyperthyroidism, peripheral vascular disease, and hypertension. The patient describes an inability to ambulate over the last few days prompting her ED visit. Prior to this, she had been able to walk without assistive devices. She denies trauma, fevers, chills, nausea, vomiting, chest pain, shortness of breath, numbness, weakness, or skin changes. She has no history of deep vein thrombosis (DVT) or pulmonary embolism, has not had recent surgery or travel, and does not use intravenous drugs or immunosuppressive medications.

Pertinent Physical Exam: Initial blood pressure was 135/73, heart rate 108 beats per minute, temperature 37.1°C, and oxygen saturation was 94% on room air. She was in no distress, breathing comfortably, heart and lung sounds were normal. Her left hip had significantly decreased range of motion secondary to pain but she had normal range of motion at the knee and ankle joints. There was significant pitting edema from her left foot to the hip while her right lower extremity had no swelling. Both extremities were warm, with equal pulses, neurologically intact, and had no skin changes.

Pertinent Laboratory Data: Laboratory evaluation revealed a white blood cell count of 14.7 cells/µL and D-dimer elevated to 7.03 mg/L. X-rays showed degenerative changes. Lower extremity duplex was unavailable to evaluate for a DVT prompting a CT-angiogram of the abdominal aorta with lower extremity runoff instead. No DVT was identified, however the CT revealed a rim-enhancing collection within the left iliiopsoas muscle, fluid in the left iliopsoas tendon sheath, and a left hip joint effusion, all concerning for iliopsoas abscess and septic arthritis (figure 1). MRI also showed evidence of iliopsoas bursitis.

Case Discussion: Psoas abscesses and septic arthritis are rare but potentially fatal entities with mortality rates of 2.4-19% and 4-42%, respectively. (1-4) Psoas abscesses present with pain in 91% of cases, usually located in the flank, back or lower abdomen, and fever in 75% of cases. (5) Septic arthritis typically presents with a swollen, erythematous joint with decreased range of motion. (6) Neither typically present with such significant pedal edema. It is known that expansion of the iliopsoas bursa can lead to pedal edema through compression of the iliac veins. (7) Further, according to cadaveric studies, 10-15% of individuals have a connection between the retroperitoneal space (where the iliopsoas muscle resides) and the hip joint via the iliopsoas bursa. (8) Given the CT and MRI findings, likely her infection spread from the iliopsoas abscess to the hip joint via the iliopsoas bursa (causing expansion) or vice versa, leading to her significant pedal edema.

However, in the setting of unilateral leg swelling without infectious signs or symptoms, many clinicians would likely first consider ruling out a DVT. This patient has a Wells Score of 3 (table 1), indicating a high pre-test probability for DVT. (9) Most societies recommend compressive ultrasound (with repeat study in one week if initially negative) as the test of choice. (10, 11) Given the extent of this patient’s edema, a proximal iliofemoral thrombosis was a likely possibility so proximal imaging, such as CT, should be considered, especially if an ultrasound study is negative. (12) Proximal imaging techniques would also allow for alternate diagnoses and causes of deep vein compression such as psoas abscesses.

The patient ultimately received open operative drainage of the abscess and washout of her left hip. She was treated with antibiotics for four weeks, entered rehabilitation, and ultimately regained her previous mobility.

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[6] Margaretten ME, Kohlwes J, Moore D, Bent S. Does this adult patient have septic arthritis? JAMA. 2007;297:1478-88.
[7] Yukata K, Nakai S, Goto T, et al. Cystic lesion around the hip joint. World J Orthop. 2015;6:688-704.
[8] Chandler SB. The iliopsoas bursa in man. The Anatomical Record. 1934;58:235-40.
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[11] Bates SM, Jaeschke R, Stevens SM, et al. Diagnosis of DVT: Antithrombotic Therapy and Prevention of Thrombosis, 9th ed: American College of Chest Physicians Evidence-Based Clinical Practice Guidelines. Chest. 2012;141(2 Suppl):e351S-e418S.
[12] Liu D, Peterson E, Dooner J, et al. Interdisciplinary Expert Panel on Iliofemoral Deep Vein Thrombosis (InterEPID). Diagnosis and management of iliofemoral deep vein thrombosis: clinical practice guideline. CMAJ. 2015;17;187(17):1288-1296