Primary Iliopsoas Abscess in an Infant: A Case Report.

Primary iliopsoas abscess (IPA) is rare in the infantile period. However, if treatment is not initiated soon, aggressive, and adequate, there is high risk for mortality or permanent damage to the hip joints. We present the case of a preterm neonate who presented at 2 months of age with swelling and restricted movements of the left leg for the past 1 week. A diagnosis of idiopathic left IPA was made due to Staphylococcus aureus which was drained surgically and treated with systemic antibiotics. Currently, the baby is 6 months old with no evidence of any sequelae.

INTRODUCTION

Iliopsoas abscess (IPA) is not a frequently encountered entity in the early infantile period.[123] Most of these cases are secondary and a primary abscess is exceptionally rare.[45] The usual presentation is reduced limb movements associated with swelling in the femoral triangle area.[5] A primary abscess is due to a hematogenous spread from bacteremia and secondary abscess occurs as a result of direct spread of infection from an adjacent structure.

CASE REPORT

This 32-weeker, preterm, 1.6-kg male baby presented at 2 months of age with complaints of swelling over the left thigh and reduced limb movements for the past 6 days. The baby had a history of respiratory distress during neonatal period for which the baby received respiratory support and antibiotics along with intravenous fluids and was discharged at 1 month of age. The baby remained asymptomatic for 3 weeks and was thriving well. The mother noticed a swelling on the left thigh at 7 weeks of age. The next day, the baby received schedule vaccination following which the mother noticed increase in the swelling size, reduction of movements of left thigh, redness, and restricted movement along with lethargy and poor feeding. There was no history of any trauma or fever.

On examination, there was a swelling in the left iliac fossa with extension up to the upper thigh, near femoral triangle, and another swelling in the gluteal region [Figure 1]. There were decreased and restricted limb movements associated with redness and warmth. With the above presentation and clinical findings, possibilities such as septic arthritis of hip, injection-site abscess, and IPA were considered. However, the swelling was localized in the upper thigh and did not correspond to injection site; hence, injection-site abscess was unlikely. There was no history of trauma. Investigations showed elevated C-reactive protein (CRP) (141 mg/L) and leukocytosis (27,500/uL) with neutrophilic preponderance (56%). Ultrasonography (USG) hip was done which showed collection in the left iliac region (5.4 cm × 3.3 cm × 2.7 cm) extending to the upper thigh, involving left iliopsoas muscle and another collection around gluteus muscle with no evidence of collection in the hip joint, suggesting arthritis. Magnetic resonance imaging (MRI) was done which confirmed the USG findings [Figure 2]. The baby was started on systemic antibiotics. Surgical drainage was done by making an incision from the anterior superior iliac spine curving posteriorly along the iliac crest. The incision was deepened and muscle from the iliac bone was elevated and pus was drained from the deep plane over the ventral aspect of the iliac bone and a cruciate incision over the gluteal region for drainage of gluteal abscess. Pus showed growth of methicillin-sensitive Staphylococcus aureus. The antibiotics were continued for 14 days. The child responded well with the given treatment. At 6-week follow-up, there was no asymmetry in appearance or movements. Currently, the baby is 6 months old, well thriving, and limb movements are normal.

Figure 1

Swelling in the left femoral triangle with associated redness. The swelling extends up to the upper thigh inferiorly, inguinal ligament superiorly, and gluteal region posteriorly

Figure 2

Magnetic resonance imaging depicting the extent of abscess with involvement of iliopsoas (a), gluteal region (b), and dorsal to iliac crest (c) (black arrow)

DISCUSSION

Primary or idiopathic infantile IPA is an extremely uncommon and potentially serious condition. The patient in our case was a 32 weeker at 2 months of age and a corrected age of 40 weeks which still counts as neonatal period. The presenting symptoms of IPA include a triad of groin swelling, limitation of leg motion, and pain.[6] Clinical mimics include septic arthritis of hip, osteomyelitis of femur, traumatic injury to hip joint and surrounding structures, and abscess at vaccination site.[12] The most important differential is septic arthritis, and a poor response to antibiotics should prompt a suspicion of IPA. The clinical differentiation although difficult at times is crucial as approach differs.[7] It is important to note that septic arthritis can often cause secondary IPA.[5] Imaging with ultrasound, computed tomography (CT), or MRI helps in differentiating the above differentials. The most common causative organism is S. aureus, followed by Klebsiella and Streptococcus. Usually, the presentation is unilateral. Bilateral IPA has also been reported.[2]

Majority of IPA in infantile period are primary and a focus is not evident. The proposed hypothesis is that S. aureus which is part of normal flora of skin and nasal flora spreads hematogenously because of the immature immune system. In our case also, there was no apparent focus. The association with immunization seems a coincidence as the swelling was noticed prior to vaccination and the site of abscess did not correspond to the injection site.

Routine investigations reveal neutrophilic leukocytosis and elevated CRP. Ultrasound is the first investigation which confirms the diagnosis and also delineates the areas of collection. MRI or CT gives a better delineation of the anatomy and extent of the lesion that helps in planning drainage. Antibiotic therapy alone is insufficient and drainage is required. Ultrasound-guided percutaneous drainage is feasible; however, open surgical drainage gives a better exploration and complete drainage which we did in our case.[8] Primary IPA can present as emergency simulating septic arthritis with septicemia. Delayed treatment and inadequate drainage carry a high risk of mortality and sequelae due to damage to the joint.[39] Whether every case of neonatal IPA needs workup for immunodeficiency is unclear as most of the reported cases have not undertaken it.[12345] However, there are cases of IPA leading to diagnosis of immunodeficiency.[10] As of now, any infant with IPA should be assessed for other evidence to suggest an underlying immunodeficiency such as failure to thrive, recurrent infections, and should be kept under follow-up. In case of any evidence, appropriate workup should be undertaken.

This case merits mention due to the rarity of primary IPA in infants yet its devastating course if not aggressively treated. Early suspicion, use of appropriate diagnostic methods, and aggressive treatment can lead to normal outcomes.

Declaration of patient consent

The authors certify that they have obtained all appropriate patient consent forms. In the form the patient(s) has/have given his/her/their consent for his/her/their images and other clinical information to be reported in the journal. The patients understand that their names and initials will not be published and due efforts will be made to conceal their identity, but anonymity cannot be guaranteed.

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Conflicts of interest

There are no conflicts of interest.