Sarcoidosis is a chronic disorder that affects many body systems. The majority of cases involve the lungs, but the condition can affect any area of the body. Sarcoidosis is characterized by an abnormal immune system response that produces deposits of white blood cells and abnormal tissue cells in the affected organ. A small percentage of cases will involve some portion of the nervous system (neurosarcoidosis).

Neurosarcoidosis may affect any part of the nervous system. Sudden, transient facial palsy (facial weakness) is common with involvement of cranial nerve VII. Any nerve can be affected, including the nerves of the eye and the nerves that control taste, smell, or hearing.

The condition can also affect a part of the brain called the hypothalamus, which is involved in regulating many body functions such as temperature, sleep, and stress responses. Muscle weakness or sensory losses can occur with peripheral nerve involvement. Other areas of the brain or the spinal cord may also be involved. Neurosarcoidosis can cause permanent disability and, in some cases, death.

Sarcoidosis occurs in highly variable groups. In the U.S. it is more common in African-Americans, while in Europe it is more common in Caucasians. The disorder is slightly more common in people 25 to 50 years old, particularly women, but can occur at any age and to either sex. It is very rare in children. When it does affect children, sarcoidosis usually involves the lungs.