An 11-day-old, full-term male presents to the emergency department (ED) with a 2-day history of decreased range of motion of his right upper extremity.
This patient was born to a 32-year-old G1P1 mother via induced vaginal delivery at 39 weeks’ gestation. Birth weight was 2955 g (19th percentile); length, 50 cm (44th percentile); and head circumference, 32 cm (9th percentile). Maternal blood group is B Rh-negative, antibody negative. Maternal group B Streptococcus (GBS) was unknown at birth but later noted to be positive by Obstetrics and not treated prior to birth. The patient’s neonatal course was complicated by hyperbilirubinemia, requiring 1 day of phototherapy.
Since discharge from the hospital, the infant has reportedly been moving his arm without difficulty until 2 days prior to presentation. According to the parents, he continues to use his hand and wrist but will not move the elbow or shoulder. There is no known trauma to the right upper extremity and no previous invasive medical procedures aside from a heel stick for routine newborn screening labs along with an uncomplicated circumcision. The family denies erythema, swelling, or increased warmth in the right arm or shoulder. He is acting appropriately, tolerating cows’s milk formula along with breast milk, and having normal wet diapers and stools. Newborn genetic screening is normal.
Physical exam and laboratory testing
The initial physical exam reveals temperature of 97.7°F; heart rate, 176 beats/minute; respiratory rate, 31 breaths/minute; blood pressure, 85/56 mm Hg; and SpO2 of 96% on room air. He is in no acute distress and is able to move his right hand and wrist. There are no spontaneous or active movements of the right elbow or shoulder, although there is normal passive range of motion. He has a normal right palmar grasp but an asymmetric Moro reflex with limited range of motion of the right shoulder and right elbow. There is no tenderness, swelling, crepitus, or deformity of the right shoulder.
Laboratory evaluation shows white blood cell (WBC) count of 17,300 x 109/L for age (lymphocytes, 34%; neutrophils, 55%; monocytes, 10%); platelets, 262,000/μL; hemoglobin, 14.6 g/dL; and hematocrit, 43%. Erythrocyte sedimentation rate (ESR) and C-reactive protein (CRP) are both elevated at 54 mm/h and 90 mg/L, respectively. Further laboratory tests are unremarkable including serum electrolytes, glucose, urinalysis, and cerebrospinal fluid (CSF) studies.
Initial differential diagnosis on admission to the neonatal intensive care unit (NICU) included, but was not limited to, brachial plexus palsy, neonatal stroke, intraventricular hemorrhage, fracture, nonaccidental trauma, osteomyelitis, herpes simplex virus (HSV) encephalitis, and septic arthritis (Table). Because of concern for acute infection in an 11-day-old infant, the patient was started empirically on intravenous (IV) ampicillin, cefepime, and acyclovir after obtaining urine, blood, and CSF studies. Ampicillin was initiated to cover gram-positive organisms including GBS and Listeria, cefepime for Escherichia coli and methicillin-sensitive Staphylococcus aureus, and acyclovir for HSV.
Initially, the main differentials were brachial plexus palsy versus acute intracranial process. A head ultrasound was performed, which was negative. Subsequently, magnetic resonance imaging (MRI) of the head and cervical spine was obtained, not under sedation or general anesthesia, and found to be significant for a small subacute subdural hematoma in the posterior fossa bilaterally without significant mass effect. The cervical MRI was poor quality because of movement. The results were discussed with Pediatric Neuroradiology and Neurosurgery and were thought to be secondary to the birthing process and likely not contributing to the decreased range of motion of the right upper extremity.
With negative intracranial pathology as the cause for the acute presentation, there was concern for acute osteomyelitis of the right upper extremity versus brachial plexus palsy. An MRI of the shoulder and neck was obtained for elevated inflammatory markers. The MRI of the neck was negative; however, MRI of the shoulder was significant for increased T2 signal in the right humeral head that extended across the physis into the metaphysis of the right humerus and mild synovial thickening (Figure).
The diagnosis of right acute humerus osteomyelitis was made.