A neonate with multiple hand flexor tendon ruptures due to methicillin-susceptible Staphylococcus aureus sepsis: a case report

Pyogenic tenosynovitis is caused by bacterial infection of the synovial sheath, resulting in finger dysfunction and, in severe cases, amputation [1, 2]. Because there are no detailed reports on pyogenic tenosynovitis in neonates, the pathogenesis, diagnostic method, progression, and prognosis of the disease in these patients remain unclear. We treated a neonate who developed multiple pyogenic tenosynovitis caused by methicillin-susceptible Staphylococcus aureus (MSSA), thought to have invaded through the needle puncture used for infusion. In this case, ultrasonography (US) was essential to diagnose pyogenic tenosynovitis. Furthermore, late-onset osteomyelitis of the proximal end of the right radius and ulna was detected by weekly radiography. After antibiotic treatment, flexor tendon rupture was found on another finger during follow-up US. A two-stage flexor tendinoplasty was completed at the age of 2 years and 1 month. We discuss the case of pyogenic tenosynovitis in a neonate with onset on postnatal day 7. This report details the diagnostic examination and treatment of the patient, including plastic surgery.

We presented a rare case of a preterm neonate with pyogenic tenosynovitis, which led to multiple finger flexor tendon ruptures, arthritis, and osteomyelitis. Intravenous antibiotics should be administered within 24 h of the onset of symptoms because delayed treatment can worsen the prognosis, including dysfunction such as limited range of motion of finger joints and amputation [1‐3]. Since there are no reports of neonates, data from adults indicate that complications occur in 38% of pyogenic tenosynovitis, including stiffness, deformity, deep infection, adhesions, persistent infection, tendon necrosis [2], and tendon rupture after infection [4, 5]. Poor prognostic factors include beta-hemolytic group A streptococci, and delayed surgical management [6]. The most common cause of pyogenic tenosynovitis is secondary to trauma including local inoculation via lacerations, puncture wounds, and bites, and is the most common route of bacterial entry [1]. Other risk factors include immunodeficiency and immunosuppression, smoking, and joint diseases, such as rheumatoid arthritis [1, 6, 7].

The pathogen involved in this case was Staphylococcus aureus, the most common bacteria identified in pediatric osteoarticular infections [8]. The suspected site of primary infection was the insertion site of the infusion needle. In Japan's NICU, wiping the puncture site with a packet of cotton impregnated with 80% ethanol before administering the infusion is standard practice. Preterm infants are at risk of skin infections because of the thin keratin and poor epidermal barrier [9]. The skin barrier takes 2–4 weeks to fully mature [10]. Skin sterilization before and after securing the intravenous route may have been insufficient in this case. Infections may be fatal for neonates [11]; thus, it is important to avoid infusion whenever possible and start enteral nutrition early to minimize infections from infusion needle insertion.

MSSA was detected in blood and synovial fluid cultures, and CRP was significantly elevated on admission. However, procalcitonin was minimally increased, and white blood cell counts were within the normal range for a preterm neonate. Serum PCT levels rise quickly but fall within the normal range within the first 72 h of life, after which time adult diagnostic criteria for bacterial infection can be used [12]. The PCT value was less than 2.0 ng/mL, the level indicative of severe sepsis [13]. These laboratory data suggested that, while the local infection was potent, the systemic infection was less aggressive. However, bacteremia may have resulted in multiple infection lesions and subsequently caused overt DIC. Inactivity and apnea of preterm infants are seen in severe medical conditions and are not specific to sepsis.

Congenital immunodeficiency was suspected because of severe, concurrent local infections. However, the tests for cell-mediated and humoral immune reactions yielded normal results. The hypocomplementemia on admission was also transient. Moreover, this case had no subsequent recurring infections or family history. Therefore, immune deficiency was not considered in this case. Genetic testing may be a better option if a patient has subsequent recurring infections or family history because diagnostic values of the test for determining immunodeficiency are not very sensitive.

US is an essential test for diagnosing pyogenic tenosynovitis with a sensitivity of 94% and a negative predictive value of 97% [14]. It was used to establish the diagnosis of pyogenic tenosynovitis in our case. Due to the tiny fingers of the preterm infant, the ultrasonographer used a high-frequency linear probe with a center frequency of 24 MHz for diagnosis. A hockey stick probe with a center frequency of 22 MHz was also used to observe the area in detail. The higher the ultrasonic frequency, the greater the attenuation, but the better the directivity and resolution, the more it is suitable for observing finger joints. The left FPL tendon had a chronic rupture. In such cases, US should be repeated if symptoms, such as limited range of motion, persist. US is also highly accurate in the early diagnosis of pyogenic arthritis. Floaters in the joint fluid seen in this case is a finding suggestive of infectious arthritis [15]. US is essential for the diagnosis of infected foci in soft tissue infections.

VCM, in conjunction with cefepime, cefotaxime, ceftriaxone, or gentamicin, is the recommended antimicrobial agent for neonatal soft tissue infections with systemic manifestations, such as bacteremia [16, 17]. As the infection in this case was hospital-associated, MEPM and VCM were initially selected. These antibiotics cover a wide range of gram-positive and gram-negative bacteria, including MRSA. However, after MSSA was identified, FMOX was prescribed instead. FMOX is a parenteral oxacephem antibiotic with high tissue transferability. It has a strong antibacterial effect against Staphylococcus aureus [18] and was thus administered as a single agent based on susceptibility. FMOX has been used in neonates and is a safe antimicrobial agent with few side effects [19].

When systemic signs, such as bacteremia or spread to adjacent structures are present, antibiotic treatment of pyogenic tenosynovitis typically takes four to six weeks. In this case, sepsis, pyogenic tenosynovitis, and pyogenic arthritis preceded the onset of the disease. Therefore, we initially planned four weeks of antibiotic treatment. However, osteomyelitis became apparent on weekly follow-up radiography during the 4^th week. In infants, pyogenic osteomyelitis is caused by hematogenous transfer or direct entry of bacteria into the bone marrow. Imaging findings may not appear in children until two weeks after onset [20]. Therefore, radiographic follow-up is essential for its detection. Pyogenic osteomyelitis is also treated for four to six weeks [8]. Thus, intravenous antibiotics were administered for another two weeks, followed by oral antimicrobial agents for four weeks.

Surgical repair of the right index finger started at the age of 1 year and 11 months. It was completed at the age of 2 years and 1 month due to the infection of the right index finger after silicone rod insertion. Two-stage tendon reconstructions are commonly performed in adults [21]. The range of motion of the joint has almost completely recovered, and the patient is being followed-up.

The limitations of this report include the inability to submit a culture of fluid stored in the tendon sheath due to the small puncture space. Additionally, our institution did not have the resources to confirm pathological changes.

Neonatal pyogenic tenosynovitis is a highly emergent soft tissue infection. Despite the absence of immunodeficiency disease, it may be secondary to a severe bacterial infection, spread hematogenously against therapeutic intervention, leading to multiple tendon ruptures. When sepsis is suspected, close observation of skin changes and evaluation of joint motion are crucial. In case of joint or subcutaneous tissue swelling and restriction of joint motion are observed, US is useful for diagnosis. In addition, it is important to refer the patient immediately to a neonatal inpatient facility where a pediatric orthopedic surgeon can provide appropriate care to implement drainage, and subsequent treatment can be performed. Furthermore, long-term follow-up for the progression of joint lesions is important even after curing sepsis.”