P0905 - Weakness and Irritability in 12-week-old Infant

Presentation
12-week-old, term female was brought to the hospital for irritability, progressively worsening reduced left upper extremity movement and left neck swelling.
10 days prior to presentation, she developed irritability with movement, especially when cradled on her left side. She was seen at urgent care; chest X-ray was performed and was read as normal. She was seen again at her primary care office for worsening fussiness; parents were again reassured and sent home.
4 days prior to her presentation, parents noted that she was not moving her left arm. On the day of admission, her parents noticed left neck swelling in addition to upper extremity weakness. She was seen in the emergency room. Non-accidental trauma (NAT) was suspected and evaluation including skeletal survey and CT head were performed.
Her vital signs on admission were significant for high blood pressure (132/86). Weight was at the 50th percentile. Examination demonstrated an ill and non-toxic appearing infant with a left anterior cervical mass, hypotonia with decreased movement of left upper extremity and lower extremity weakness bilaterally with hypotonia. The reminder of the exam was unremarkable.
Labs were unremarkable. Skeletal survey demonstrated a left apical mass (image 1). MRI (image 2) showed a large mass within the left neck encasing subclavian and vertebral arteries, encasing the left brachial plexus, and extending into the spinal canal causing cord compression.

Discussion
History, physical and diagnostic evaluation were concerning for tumor with spinal cord compression. She was admitted to the oncology service and received dexamethasone for cord compression. Biopsy of the mass was performed. Emergent chemotherapy was started with pathology pending due to spinal cord compression. Within 24 hours of initiating chemotherapy and steroids, neurologic symptoms were improving.
Pathology results confirmed a diagnosis of malignant rhabdoid tumor

Conclusion
Infants presenting with an immobile arm and neck mass maybe thought to have a benign condition in primary care settings. Differential diagnoses of arm weakness include injuries including NAT, neuropathies; congenital or acquired and rarely neoplasms. Neck mass in infants can be congenital (e.g. branchial cleft cyst, cystic hygromas, hemangiomas) or acquired (e.g. lymphadenopathy, malignancy).
Our 12-week old patient presented with irritability and worsening weakness of the left upper extremity along with a left apical mass with spinal cord compression. This constellation of findings represents an oncologic emergency. Biopsy confirmed malignancy, rhabdoid tumor; a rare, highly aggressive neoplasm with poor prognosis.
This case highlights the importance of a careful history, physical exam, and imaging when evaluating an infant with weakness at the primary care setting. Though rare, it is critical to consider tumors in the differential when evaluating an infant with weakness with or without associated mass lesions.