Abstract
Atlantoaxial subluxation (AAS), while uncommon in the general population, occurs more frequently in children with Down syndrome (DS). This association is attributed to the presence of connective tissue laxity, which affects approximately 15-20% of individuals with DS. A 12-year-old female patient with known classical DS presented to a healthcare institution with complaints of vomiting and inability to walk. Physical examination revealed moderate to severe intellectual disability and limited verbal communication. Facial features included DS characteristics such as low-set ears and a flattened nasal bridge. Neurologic examination demonstrated weakness in the left upper and lower limbs (1-2/5 on muscle strength testing), increased deep tendon reflexes on the left side, and an extensor plantar response (Babinski sign). Neuroimaging studies revealed no cranial abnormalities. Brain MRI, however, demonstrated an increased atlantoaxial joint distance (10 mm) on the sagittal image, suggestive of AAS. Additionally, the MRI showed anterior compression of the odontoid process on the spinal cord, indicating potential for spinal cord compression. While cerebrovascular events are the most common cause of hemiparesis, health professionals should keep in mind AAS as a potential culprit in DS patients with limited communication and cognitive abilities. In such cases, prompt investigation and evaluation are essential, as early surgical intervention can significantly improve outcomes and prevent permanent neurological damage. This case highlights the importance of considering the specific needs and challenges faced by DS patients in the diagnostic and therapeutic process.

Key words: Down syndrome, Atlantoaxial subluxation, Hemiparesis, Neuroimaging.