Peripheral Neuropathy

Peripheral nerve dysfunctions (trigeminal nerve in this case) can occur due to variety of reasons.

Most common causes are vitamin deficiency, diabetes mellitus, excessive alcohol intake, lead poisoning. There are myriad other causes of peripheral neuropathy.

Electrolyte Imbalances (abnormal blood levels of calcium or potassium or sodium) can also result in nerve dysfunction.

Multiple Sclerosis

Autoimmune damage to outer protective covering of the nerves (myelin sheath) results in multiple sclerosis.

Symptoms are highly variable depending upon the segment of nervous system involved.

MS afflicting trigeminal nerve or brain regions handling facial sensations can result in numbness of the face.

Nerve Injury (Trauma, Positional)

Injury to the various branches of the trigeminal nerve can cause facial numbness.

Usually, when only a specific branch is injured, the area of numbness is confined to the region of the face innervated by that branch.

Nerve injury can occur due to trauma or sleeping in awkward position (resulting in prolonged compression of the nerve).

Migraine

The aural phase and/or the prodromal phase of the migraine can have numbness in face as one of the symptoms.

Less commonly, facial numbness can persist or occur exclusively during the headache phase.

Transient Ischemic Attack

TIA or "mini-stroke" occurs when blood flow to a part of brain is interrupted for a short period of time.

TIA can present with variety of symptoms depending upon which part of the brain is affected. TIA involving the region of brain handling facial sensations can result in brief period of facial numbness. Often, other symptoms are also present.

Usually there is full recovery after an attack with no neurological deficit or brain damage. However, TIAs are warning signs of an impending stroke that may occur anytime.

Stroke

Stroke can result in facial numbness. However, other more severe symptoms like paralysis, or altered consciousness, etc. dominate the presentation of the stroke.

Brain Tumors

Brain tumors can result in facial numbness.

Numb Chin Syndrome

Numbness is confined to chin region.

Usually caused by trauma, but can occur in cancers also when they spread to the jaw bone and invade the nerve innervating the chin region. (e.g. acute myeloid leukemia, prostate adenocarcinoma, osteoblastic osteosarcoma, breast cancer and many more)

Trigeminal Neuralgia

A "seizure" occurring in the trigeminal nerve.

Rarely trigeminal neuralgia can result in numbness in face. However, facial numbness preceding the intense pain is more likely to occur.

Shingles

Shingles or herpes zoster can rarely have facial numbness in the prodromal phase (i.e. before the appearance of painful skin blisters).

However, more commonly pain and paraesthesias occur in the prodromal phase.

Nerve Tumors or Invasion of nerve by tumors

Trigeminal nerve (including branches) tumors (e.g. Schwannomas) or invasion of the nerve by nearby tumor (e.g. Meningioma) can result in facial numbness.

Focal Seizures

Seizures confined to areas of the brain handling facial sensation can result in facial numbness.

Hypothyroidism

Facial numbness can occur in hypothyroidism. Other symptoms of hypothyroidism will dominate the presentation.

Psychogenic  conditions

Stress, depression and panic attacks can result in facial numbness.

Idiopathic cases

Sometimes no cause can be found even after thorough neurological evaluation. Such cases are referred to as idiopathic cases.