Rethinking Limp Diagnosis: Brodie’s Abscess Linked to Streptococcal Infections

Introduction

Brodie’s abscess was first described in 1832 by Sir Benjamin Brodie as a localized form of subacute osteomyelitis [1]. It predominantly affects children 2–15 years of age, with a slight male predominance, although it has been seen in adults as well [2]. The condition commonly presents with an insidious onset of symptoms that include mild-to-moderate pain with few to no constitutional symptoms and no known previous acute disease [2,3]. The lower limbs, especially the tibia, are more frequently affected than the upper limbs, with the metaphysis being the most commonly involved site [4,5].

Due to the rarity of the illness and the slow progression of symptoms, there is often a delay from the initial presentation of pain to diagnosis [3,6]. The initial workup of this condition often shows normal or near-normal inflammatory markers (WBC, CRP, ESR) and X-ray imaging is often negative [5,7]. However, should X-rays reveal a bone lesion, it is most often mistaken for a tumor. Historically, when a child presents with unilateral limb pain, standard imaging with plain film or ultrasound are performed, with progression to arthrocentesis as needed. However, further imaging with MRI has become the criterion standard for diagnosis [8]. Once identified, treatment often includes surgery and a prolonged course of antibiotics to address gram-positive organisms, of which Staphylococcus aureus is the most commonly grown on culture [3,6,9]. Treatment is known to be curative, with low rates of recurrence or disability [3,5].

We describe a case Group A Streptococcus (GAS) pharyngitis resulting in a Brodie’s abscess, which to the best of our knowledge has not been previously reported.

Case Report

A previously healthy 6-year-old boy began having a sore throat (day zero). On day 4, he was seen by his pediatrician and was started on amoxicillin for treatment of streptococcal pharyngitis, which was confirmed with a rapid streptococcal antigen test. On day 6, he began having left knee pain. He was unable to walk on day 7 and presented to the ED with fever, atraumatic left knee pain (FACES Pain Scale of 8), swelling, and decreased ROM (Table 1). In the ED, he had an elevated temperature of 38°C and tachycardia at 111 beats per minute. Physical examination demonstrated that the left knee was warm to the touch, with diffuse swelling, severe pain with ROM, and a joint effusion with no overlying skin changes. Inflammatory markers included: WBC 11.0 k/uL (normal range 5.00–14.50), ESR 48 mm/h (normal range <15), and CRP 190.2 mg/L (normal range 0.1–1.0). His knee X-rays were negative (Figure 1), while the left knee ultrasound showed a moderate knee effusion. Arthrocentesis was performed in the ED, with initial results suggesting septic arthritis (nucleated cell 19 148, 93% neutrophils, 5% lymphocytes, 1% macrophages/histiocytes, RBC 139 592). He was then admitted to the hospital for IV antibiotics and MRI. MRI found a subperiosteal abscess extending about 6 cm along the length of the posterior distal femur (Figure 2). Orthopedic Surgery was consulted, and the patient was taken to the operating room for debridement and drain placement. Wound cultures from debridement grew Streptococcus pyogenes (GAS). The synovial fluid culture did not grow any organisms.

The patient was initially started on clindamycin IV and then transitioned to oral cephalexin (a 28-day course) and discharged home with a Jackson-Pratt drain in place on day eleven. While home, the patient had significant improvement on the antibiotic regimen and the drain was removed. On day 22, 11 days after discharge home and while still on oral cephalexin, he returned to the ED with 1 day of recurrent left knee pain (FACES Pain Scale of 2). On physical examination, the knee was noted to have swelling, warmth, and decreased ROM. At that time, blood results showed WBC 8.03 k/uL, ESR 66 mm/h, and CRP 13.8 mg/L. Due to concern for recurrent infection, he was admitted for clindamycin IV, with Orthopedic Surgery consultation. A repeat MRI on day 24 confirmed development of a subacute distal femur osteomyelitis with intraosseous abscess (Brodie’s abscess) and recurrent subperiosteal abscess (Figure 3). He went for surgical debridement twice during this hospitalization, on days 25 and 28. All subsequent cultures had no growth, likely due to continued use of antibiotics. He was transitioned to oral clindamycin (a 30-day course) and discharged home on day 31, with complete resolution of symptoms at 2-month follow-up.

Discussion

Our patient presented to the ED with a painful swollen knee, which was initially presumed to be septic arthritis after a recently confirmed Group A Streptococcus (GAS) pharyngitis. Workup with inflammatory markers (CBC, CRP, ESR), X-rays, ultrasound, and arthrocentesis were all inconclusive. Only with an MRI were we able to make the diagnosis of Brodie’s abscess. Although he had a complicated course with IV antibiotics and multiple surgical debridements, the patient finally made a full recovery. Historically, workup for a child presenting with a limp includes X-rays, inflammatory markers, and arthrocentesis to diagnose a septic joint [10]. The differential diagnosis for a child with a limp includes transient synovitis, juvenile idiopathic arthritis (JIA), osteomyelitis, Lyme disease, trauma, reactive arthritis, Kawasaki disease, rheumatic fever, bone tumors, slipped capital femoral epiphysis (SCFE), and, depending on the affected joint, Legg-Calvé-Perthes disease (especially in the hip). Many of these diagnoses can be ruled out by history, physical exam, inflammatory markers, and X-ray.

Unfortunately, due to the current increase in invasive GAS infections, clinicians also need to consider osteomyelitis and periosteal abscess. To fully elucidate the cause of symptoms, MRI is the most appropriate method for assessment of septic arthritis and osteomyelitis in children [8]. Our case highlights a rare complication of GAS pharyngitis resulting in a subacute osteomyelitis (Brodie’s abscess) and the importance of performing MRI to make the correct diagnosis.

In 2023, the incidence of invasive GAS was at a 20-year high [10]. When properly treated, streptococcal pharyngitis usually resolves without incident. However, there have been multiple known sequelae of GAS infections such as rheumatic fever/heart disease, retropharyngeal abscesses, sinusitis, reactive arthritis, and glomerulonephritis.

In addition to surgical debridement, antibiotic administration is the standard of care for Brodie’s abscess. In patients with Brodie’s abscess, Staphylococcus aureus was the pathogen most often found in the abscess culture (67%), none of which were methicillin-resistant, and Group A Streptococcus was found in 7.5%. Therefore, our patient was treated with clindamycin. An abscess recurrence rate of 15.6% has been reported, requiring further intervention [3]. Some authors suggest that these infections can develop from bacteria carried by the blood stream reaching the subperiostium secondary to blunt trauma, or as a severe form of septicemia [3]. Some authors have proposed that Brodie’s abscess can be caused by hematologic spread from otitis media or pharyngitis, but this has never been proven [11]. Brodie’s abscess has been shown to be caused by GAS secondary to trauma, postpartum, and, potentially, via hematologic spread; but to the best of our knowledge our case of Brodie’s abscess is the first that was preceded by a recently documented GAS pharyngitis [12,13].

Conclusions

Historically, the workup for a limping child included a septic joint, but today, due to the increase in invasive Group A Streptococcus (GAS) infection, we also need to consider osteomyelitis and periosteal abscess.

In this case report, we demonstrate a previously undocumented cause of subacute osteomyelitis in children, also known as Brodie’s abscess. This is significant because subacute osteomyelitis has been known to be mostly caused by Staphylococcus aureus and usually without a preceding illness or known cause. Our patient had a previous infection with GAS pharyngitis, and a culture confirmed Brodie’s abscess secondary to GAS. Given the increase in invasive GAS, it is important that providers consider alternative complications and sequelae of these infections. In most cases involving limping children, imaging stops at plain films or ultrasound to evaluate fracture, and then an arthrocentesis is performed to rule out a septic joint. Due to increased rates of invasive GAS, imaging with MRI is the criterion standard and should be considered to rule out osteomyelitis and subacute osteomyelitis (Brodie’s abscess). This case report will assist healthcare professionals in broadening their differential diagnosis and to use MRI in evaluating pediatric patients with a limp.