How is Pendred syndrome diagnosed?
A physician called an otolaryngologist or a clinical geneticist will consider a person's hearing, inner ear structures, and sometimes the thyroid in diagnosing Pendred syndrome. The specialist will evaluate the timing, amount, and pattern of hearing loss. He or she will ask questions such as:
- "When did the hearing loss start?,"
- "Has it worsened over
- "Did it happen suddenly or in stages?."
Early hearing loss is one of the most common characteristics of Pendred syndrome; however, this symptom alone does not mean a child has the condition.
The specialist uses inner ear imaging techniques known as magnetic resonance imaging (MRI) or computed tomography (CT or CAT) to look for two key characteristics of Pendred syndrome. One characteristic might be a cochlea with too few turns. The cochlea is the spiral-shaped part of the inner ear that converts sound into electrical signals that are sent to the brain. A healthy cochlea has two-and-a-half turns, but the cochlea of a person with Pendred syndrome may have only one-and-a-half turns.
A second characteristic of Pendred syndrome is enlarged vestibular aqueducts (see figure). The vestibular aqueduct is a bony canal that runs from the vestibule (a part of the inner ear between the cochlea and the semicircular canals) to the inside of the skull. Inside the vestibular aqueduct is a fluid-filled tube called the endolymphatic duct, which ends at a balloon-shaped endolymphatic sac. When the vestibular aqueduct is enlarged, the endolymphatic duct and sac grow large with excess fluid in comparison to their normal sizes. The function of the vestibular aqueduct is not well understood.
Picture of the Inner Ear
When screening for Pendred syndrome, it is not recommended to test the blood for thyroid hormone because the amount usually is the same whether someone has Pendred syndrome or not. Some people may receive a "perchlorate washout test," a test that determines whether the thyroid is functioning properly. Although this test is probably the best test for determining thyroid function in Pendred syndrome, it is not used often and may be replaced by genetic testing. Individuals who have a goiter may be referred to an endocrinologist, a doctor who specializes in glandular disorders, to determine whether the goiter is due to Pendred syndrome or to another cause. Goiter is a common feature of Pendred syndrome, but many individuals who develop a goiter do not have Pendred syndrome. Conversely, many people who have Pendred syndrome never develop a goiter.