Volume 5, Case 11
Rodney B. Boychuk, MD
Kapiolani Medical Center For Women And Children
University of Hawaiʻi John A. Burns School of Medicine
This 11 year old male was in good health until 6 days ago when he began to have right hip pain at rest, which worsened with walking. The pain was described as intermittent in nature. It did not radiate to the back or down the leg. It was described initially as being of medium severity, worsening when moving from side to side and with walking. The pain progressively increased in intensity. Five days ago, the patient was seen by a pediatrician and an orthopedic surgeon. Pelvic radiographs were done (including hips). These were interpreted as normal. WBC was elevated at 25,600 and his ESR was elevated at 88. A UA was normal. The patient was observed and treated with acetaminophen for pain, which appeared to help somewhat. Yesterday when the patient awoke, he was unable to bear any weight on his right leg and could not walk. There was no past history of significant trauma, unusual physical activity, or definite fever. He did have a history of a sore throat, with fever up to 39.5 degrees, vomiting x1 with diarrhea x1 three days prior to the onset of this hip pain.
Exam: VS T38, P102, RR 20, BP 126/89. Weight 54 kg (greater than 95th percentile), height 138 cm (25th percentile). He is lying down eating a cookie in no distress. There are no mouth lesions or palatal petechiae. The posterior pharynx is non-erythematous; however, the tonsils are slightly enlarged, without any exudates. Heart regular without murmurs. Lungs clear. Abdomen is soft and somewhat obese. There is definite right lower quadrant tenderness with palpation. There is no rebound tenderness. Bowel sounds are active. Definite right-sided pelvic pain is elicited with attempts to rotate the pelvis; however, there was no pain with either internal or external rotation of the hip joint. Hip flexion and extension do not elicit any significant pain; however, straight leg raising elicits pain. There appears to be some tenderness along the right lumbar area just lateral to the lumbar spine (paraspinal area) and over the posterior region of the iliac crest with palpation. He is unable to bear weight on the right leg. The left hip appears totally normal. His neurologic exam is unremarkable.
A repeat sed rate is 62, and the following radiographs are ordered: 1) pelvis including hips, 2) abdomen, and 3) lumbar spine.
View radiographs.
Only the flat plate of the abdomen is shown here. All of these radiographs are initially interpreted as normal (note that retrospectively, there is a scoliosis to the right in the abdominal films and one might consider that there is a right lower quadrant sentinel loop present).
Because of persistence of these physical findings, a CT scan of the abdomen is done with both oral and IV contrast administration.
View abdominal CT scan.
The CT scan extends from the lower level of the kidneys down through the pelvis. There is enlargement of the right psoas muscle (left side of the image). There is a septated 2.0 cm hypodense area with an enhancing margin in the medial aspect of the right psoas muscle (arrow). This finding is consistent with a psoas abscess. There is a small amount of edema of the adjacent retroperitoneal fat. The appendix is filled with barium and appears normal. No other abnormalities are seen.
Overall impression: An abscess in the medial aspect of the right psoas muscle with diffuse enlargement of the muscle. The abscess is situated just inferior to the lower pole of the right kidney.
Findings at surgery: The psoas muscle was diffusely edematous, but only a small amount of fluid was obtained. No well-established abscess was found. Culture of the fluid from the psoas muscle was positive for group A beta-hemolytic streptococcus.
Post-operatively, the patient developed persistent fevers, with chills and a temperature greater than 40 degrees. Initially, he was treated with vancomyin; however, because of the above, switched to penicillin and clindamycin. Clindamycin is of value in severe streptococcal and staphylococcal infections for two reasons: 1) It acts on bacterial cells at a different site than penicillin. If the bacterial cells are not actively dividing, they will not be killed by penicillin. In certain abscesses where organisms are present in high quantities, active division is not occurring for many of the organisms. 2) It has an effect of depressing harmful toxin production that may be produced by this invasive group A beta-hemolytic streptococcus.
Discussion of psoas muscle abscess in children:
Although primary psoas abscess is very rare in children of "developed" countries, it is not rare in tropic and sub-tropical "third world" countries with poor socioeconomic conditions. Staphylococcus aureus is the most frequent type of infection seen in these environments, with almost all children presenting with the triad of pyrexia, flank pain and hip symptoms.
Psoas abscess can be a secondary problem associated with tuberculous spondylitis or in relation to inflammatory bowel disease (1). More recently, in the United States, psoas abscesses have been seen secondary to transperitoneal low-velocity gunshot wounds to the spine (3), or gastrointestinal or genitourinary trauma (2). Primary psoas abscess can be seen in patients with sickle cell disease, intravenous drug users, immunocompromised individuals or individuals positive for HIV.
Bacterial infections of muscle also known as pyomyositis or tropical pyomyositis occur more commonly in tropical regions. Pyomyositis should be considered in the differential diagnosis of septic-appearing children, as well as children complaining of joint pain or muscle aches (7). Recent imaging techniques are important in diagnosis. Plain radiographs occasionally show a blurring or indistinctness of the lateral margins of the psoas muscle but, in general, are not as helpful as other techniques. Ultrasonography is useful in showing enlarged psoas muscle with hypoechogenic masses, however it is not as accurate as a CT scan in showing the abscess (5). Drainage of the abscess by CT-guided percutaneous catheter has been recommended by some (4), while surgical drainage is recommended by others, especially when percutaneous catheter drainage is not successful. MRI is advantageous because multiple processes can be evaluated (6). If the patient does not respond quickly to antibiotics and surgical intervention, either there is a recurrence of the previously debrided abscess, or there is an unrecognized secondary abscess. Multiple abscess sites should be considered prior to initial debridement.
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