Fever and Limp in a 3-Year-Old Girl

Setshedi Makwinja, MD; Ben Numpang, MD; Benjamin R. Aubey, MD, MPH

Disclosures

October 28, 2015

Discussion

As previously mentioned, the lumbosacral plain films were essentially unrevealing (see Figures 1 and 2). The MRI scan of the lumbosacral region, however, revealed a right multiloculated psoas abscess, with paraspinal extension in the region of L3-4 (see Figures 3 and 4) and possible involvement of the ipsilateral pedicle of L3 (not shown in the images provided). Osteomyelitis could not be ruled out based on the images. The abscess measured 1.1×0.6×2.5 cm.

Figure 1.

Figure 2.

A psoas abscess may be classified as primary or secondary, depending on the presence or absence of an underlying cause. In cases of primary psoas abscess, there is no identifiable source of infection. The psoas muscle is a single structure ("psoas major") in 70% of people, but the remaining 30% also have a smaller "psoas minor," which lies anterior to the psoas major and along the same course. In the lower half of the psoas muscle's course, it runs alongside the iliacus muscle, with a common tendon insertion into the lesser trochanter. Together, they are referred to as the iliopsoas. It lies in close proximity to many organs, such as the sigmoid colon, jejunum, appendix, ureters, aorta, renal pelvis, pancreas, iliac lymph nodes, and the spine. Infections in these organs can contiguously spread to the psoas muscle. A rich vascular supply is believed to predispose it to hematogenous spread from sites of occult infection.[1,2,3]

Figure 3.

Figure 4.

A psoas abscess in children classically presents as a triad of fever, limp, and hip pain. It is important to differentiate between primary disease of the hip and a psoas abscess, as close proximity of a psoas abscess to the hip capsule can result in a similar presentation. This contributes to its extreme clinical variability. Passive rotation of the hip joint in flexion is possible in cases of psoas abscess, whereas in primary disease of the hip, resistance would be likely. Dysfunction of this joint, however, widely varies, ranging from complete pseudoparalysis to normal range of motion.

In our case, the child presented with the additional finding of tenderness localized to the lower back, which led to an initial incorrect working diagnosis of diskitis. The differential diagnoses in this patient included psoas abscess, pyelonephritis (ruled out by the urine analysis), osteomyelitis, and a neoplastic process. Garner has and colleagues[4] suggested that the incidence of psoas abscess is probably underreported. Primary psoas abscess has a better prognosis than secondary psoas abscess, with a mortality rate of 2.4% (18.9% for secondary abscesses). The median time of diagnosis is 3 days, and the median hospital stay is 27 days. The major cause of death is delayed or inadequate therapy.[5,6]

The appropriate imaging studies are important to accurately diagnose this uncommon clinical presentation. Ultrasonography has been recognized as the quickest and least expensive diagnostic imaging modality, as well as being a safe one. It can also differentiate between solids and liquids but, unfortunately, has a low sensitivity. Plain films of the abdomen may show enlargement or loss of definition of the psoas muscle or gas shadows in the soft tissue. Even though findings on plain films correlate poorly with a lesion, especially given the frequent presence of overlying bowel and stool, studies have shown that plain films should be performed before other imaging modalities in patients with suspected psoas abscesses (but may not be necessary if CT scan is already planned). CT scans done with intravenous (IV) contrast show rim-enhancing hypodense areas, with secondary findings of inflammation obliterating surrounding tissue, gas bubbles, and bone destruction when present.

Marked wall thickening, rim thickening, or multiple cavities may be noted; this suggests tuberculous rather than pyogenic infection. CT scans are also useful in recognizing potential etiologies such as Crohn disease and appendicitis. MRI (which was the diagnostic study in this case) has been reported to be more sensitive than CT scanning in displaying tissue contrast resolution and in screening out bone interference, as well as showing the extent of disease. A study by Yin and colleagues[7] recommended the use of a bone scan, especially in patients presenting with low back pain and an established fever of unknown origin, as it allows detection of unexpected concomitant infections.[1,7,8]

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