Testing and Diagnosis for Idiopathic Hypersomnia

Idiopathic hypersomnia (IH) is a chronic sleep disorder. It causes people to feel very sleepy during the day. This happens even after a full night of sleep. People with IH often sleep for long periods but still wake up feeling tired. Finding out if someone has IH can take time.¹

There is no single test that proves a person has it. Instead, doctors must look at many different pieces of information.^1,2

Diagnosis of exclusion

Doctors call IH a "diagnosis of exclusion." This means they must rule out all other possible causes for the sleepiness first. Doctors only diagnose IH after they prove that nothing else is causing the symptoms.²

Doctors look for common issues like sleep apnea or thyroid problems first. They also check for narcolepsy. If no other cause explains the sleepiness, the diagnosis may be IH.²

Physical exam and health history

The first step involves a physical exam. A doctor will look at your overall health. They will ask about your medical history. This includes questions about your sleep habits.^3,4

Doctors may ask questions like:^3,4

• How long do you typically sleep at night?
• Do you feel rested when you wake up?
• Do you take naps? Are they refreshing?
• Do you have trouble waking up in the morning?

Your doctor may ask you to keep a sleep diary. With a sleep diary, you will be asked to write down when you sleep and wake up each day. This usually lasts for 2 weeks.^3,4

Doctors may also use the Epworth Sleepiness Scale. This is a short survey. It asks how likely you are to doze off during normal activities. Examples include watching TV or sitting in a car.³

Blood tests and imaging

Doctors use lab tests to check for other health conditions. These conditions can also cause fatigue. Blood tests help rule them out.²

Common tests check for:²

• Anemia (low red blood cell count)
• Thyroid problems
• Vitamin deficiencies

Sometimes doctors order imaging tests. These might include a CT scan or an MRI of the head. Doctors only use them if they suspect a brain injury or other neurological issue.²

Polysomnogram (PSG)

A polysomnogram is an overnight sleep study. It takes place in a sleep center or hospital. You sleep in a private room.^3,4

Technicians place sensors on your head, face, and body. These sensors measure many things while you sleep. They track:^3,4

• Brain waves
• Heart rate
• Breathing patterns
• Muscle activity
• Eye movements

The main goal of the PSG is to rule out other sleep disorders. It looks for sleep apnea and limb movement disorders. People with IH usually have a normal PSG result. However, they may sleep for a very long time if allowed.^3,4

Multiple Sleep Latency Test (MSLT)

The Multiple Sleep Latency Test (MSLT) is often called a "nap study." It happens the day after the overnight PSG. This test measures how fast you fall asleep during the day.^3-5

The test consists of 5 scheduled naps. These happen 2 hours apart. You lie down in a dark, quiet room for each nap. You have 20 minutes to fall asleep.^3-5

Doctors look for 2 main things during the MSLT:^3-5

• Sleep latency – This is how long it takes to fall asleep. People with IH usually fall asleep in fewer than 8 minutes on average.
• REM sleep – This is the dream stage of sleep. People with narcolepsy often enter REM sleep quickly. People with IH usually do not enter REM sleep during these naps.

Doctors may diagnose IH if you fall asleep quickly but have fewer than 2 naps where you fall into REM sleep.^3-5

Have patience

Diagnosing idiopathic hypersomnia involves many steps. It requires patience. Doctors must rule out common causes like sleep apnea and anemia first. The process can include physical exams, imaging, blood work, and sleep studies. The overnight PSG and the daytime MSLT are the most important tools. These tests help doctors confirm that IH is the correct diagnosis.^1-5