Stroke: The combination of weakness and sensory deficits in the right upper extremity (RUE) and right lower extremity (RLE) along with facial numbness is highly suggestive of a stroke, particularly one affecting the left hemisphere of the brain, which controls the right side of the body. The facial numbness could indicate involvement of the trigeminal nerve or its nuclei in the brainstem.

Multiple Sclerosis (MS): MS can present with a wide range of neurological symptoms, including weakness, sensory deficits, and numbness in various parts of the body, depending on the location of the lesions in the central nervous system. The optic neuritis and facial numbness could be part of an MS relapse.
Peripheral Neuropathy: While less likely to cause such localized and specific deficits, certain types of peripheral neuropathy (e.g., mononeuritis multiplex) could potentially cause weakness and sensory deficits in multiple limbs, though the pattern would typically be more asymmetric and the facial numbness might not fit as neatly.
Spinal Cord Lesion: A lesion in the spinal cord (e.g., due to trauma, tumor, or infection) could cause bilateral weakness and sensory deficits below the level of the lesion, but the involvement of facial numbness would be unusual unless the lesion was very high in the cervical spine or there were additional brainstem lesions.

Brainstem Stroke: A stroke in the brainstem can cause a variety of symptoms, including weakness, sensory deficits, and cranial nerve palsies, which could explain the facial numbness. Given the critical functions controlled by the brainstem, missing this diagnosis could be catastrophic.
Cervical Spine Injury or Instability: Acute injury or chronic instability in the cervical spine could lead to spinal cord compression, causing the described symptoms. This is a medical emergency requiring immediate attention to prevent further neurological deterioration.
Meningitis or Encephalitis: Infections like meningitis or encephalitis can present with a wide range of neurological symptoms, including focal deficits, and are medical emergencies.

Neurosarcoidosis: This condition, where sarcoidosis affects the nervous system, can cause a wide variety of neurological symptoms, including cranial neuropathies and lesions in the brain and spinal cord, potentially explaining the patient's symptoms.
Vasculitis (e.g., Giant Cell Arteritis, Primary Central Nervous System Vasculitis): These conditions involve inflammation of blood vessels and can cause stroke-like symptoms, including focal neurological deficits, though they are less common and might not initially be considered without other systemic symptoms.
Mitochondrial Disorders: Certain mitochondrial disorders can cause a combination of neurological symptoms, including weakness and sensory deficits, though these would typically be part of a broader syndrome with other systemic involvement.