Bell Palsy, Trigeminal Neuralgia, Meningitis, Encephalitis

These conditions range from focal cranial-nerve disorders to life-threatening inflammation of the meninges or brain. The first useful distinction is not the disease name; it is the pattern and its urgency. Bell palsy produces sudden unilateral weakness of the entire side of the face, including the forehead. Trigeminal neuralgia produces very brief bursts of severe, electric-shock–like pain, usually without sensory loss. Meningitis irritates the protective layers around the brain and spinal cord, while encephalitis disrupts brain function itself. They may occur together, but altered behaviour, seizures, memory disturbance, or a focal brain deficit should make encephalitis part of the working diagnosis. West Nile virus can cause either meningitis or encephalitis and may also produce acute flaccid paralysis. A patient with fever, headache, neck stiffness, and confusion is not a routine headache patient. A patient with a new facial droop is not automatically having Bell palsy. Pattern recognition must be paired with a search for the dangerous alternative.