Symptoms:

The primary symptom is when you temporarily stop breathing, especially during sleep. People with apnea of unknown cause may awaken frequently and complain of insomnia.

If a neurological condition is causing the apnea, it may also produce other symptoms. These include difficulty swallowing, change in voice, weakness, or numbness throughout the body, depending on the underlying disease and what parts of the nervous system it has affected.

Signs and tests:

• Lung and breathing studies
• All-night polygraphic sleep monitoring
• MRI
• Tests to diagnose an underlying medical condition