A focal neurologic deficit is a problem in nerve, spinal cord, or brain function that affects a specific location, such as the left face, right arm, or even a small area such as the tongue.

It also refers to any problem with a specific nervous system function such as memory or emotion.

The type, location, and severity of the problem can indicate the area of the brain or nervous system that is affected.

In contrast, a non-focal problem is NOT specific -- such as a general loss of consciousness.

A focal neurologic problem can affect any function:

• Movement changes include paralysis, weakness, loss of muscle control, increased muscle tone, loss of muscle tone, or involuntary movements (such as tremor)
• Sensation changes include paresthesia (abnormal sensations), numbness, or decreases in sensation

Other examples of focal loss of function include:

• Horner's syndrome: one-sided eyelid drooping, lack of sweating on one side of the face, and sinking of one eye into the socket
• Inattention to the surroundings or a part of the body (neglect)
• Loss of coordination, or loss of fine motor control (ability to perform complex movements)
• Poor gag reflex, swallowing difficulty, and frequent choking
• Speech or language difficulties such as aphasia (a problem understanding or producing words) or dysarthria (a problem making the sounds of words), poor enunciation, poor understanding of speech, impaired writing, impaired ability to read or to understand writing, inability to name objects (anomia)
• Vision changes such as reduced vision, decreased visual field, sudden vision loss, double vision (diplopia)

Anything that damages or disrupts any PART of the nervous system can cause a focal neurologic deficit. Examples include:

• Brain tumor
• Cerebral palsy
• Disorders of a single nerve or nerve group (for example, see carpal tunnel syndrome)
• Infection
• Neurodegenerative illness
• Stroke
• Trauma
• Vascular malformation