Previously Healthy 3-week-old Infant with Limited Right Arm Mobility

Abstract

A previously healthy, 3-week-old, term girl presents with a 6-day history of decreased right arm movement. She had previously been using both arms equally; however, a week before presentation, after waking her up from a nap her parents noticed that the infant's right arm was hanging limp. There was no reported history of trauma, and the infant was otherwise well appearing. The patient initially presented to an outside emergency department. There she was diagnosed as having a right elbow subluxation, and a reduction was subsequently attempted. When symptoms persisted 2 days later, her primary pediatrician directed the family to a referred medical center for further evaluation.On presentation the infant is afebrile, with normal vital signs. Examination reveals minimal movement of her right fingers, and her arm is held in an adducted, extended, and internally rotated position. Notably, palpation and manipulation of the right arm appear to induce pain, without any focal areas of tenderness. There is no swelling, warmth, or erythema of the soft tissues or joints. An asymmetrical Moro reflex is elicited and appears painful. The remainder of her physical examination findings are normal.Given the patient's apparent pain with manipulation of her right arm, a plain radiograph of the extremity is obtained to rule out a fracture. Imaging reveals her diagnosis and prompts further laboratory studies and evaluation. DISCUSSION Differential DiagnosisAt the time of initial presentation, suspected etiologies for the patient's symptoms included a fracture, a brachial plexus injury, a bone tumor, and osteomyelitis. Based on the history of paralysis of the infant's limb, a brachial plexus injury was initially considered. However, the patient was able to move both arms when a Moro reflex was elicited, albeit asymmetrically. This raised suspicion for pseudoparalysis secondary to pain from trauma.The temporal relationship between the infant's delivery and presentation effectively ruled out birth trauma as a cause of the presenting findings. Accidental and nonaccidental trauma were considered and prompted the initial radiograph.Osteomyelitis was discussed as a potential cause of the patient's pain. However, based on her lack of fever and overall well appearance on the examination, this was considered to be less likely. A bone tumor-infantile myofibromatosis in particular-was also considered.AUTHOR DISCLOSURE Drs Ajewole, Baker, Hackett, and Aprile have disclosed no financial relationships relevant to this article. This commentary does not contain a discussion of an unapproved/investigative use of a commercial product/device.