Benign intracranial hypertension (BIH) is a rare neurological side effect that has been linked to hormone-based contraceptives. This condition, which is often misdiagnosed as a brain tumor, is caused by sudden increased pressure on the brain. Signs and symptoms of BIH include blurred or double vision, headache, persistent ringing in the ears (tinnitus), and swelling of the optic nerve (papilledema).
What is Implanon?
Implanon is a hormone-carrying plastic rod that is inserted under a woman’s arm to protect against pregnancy. The device releases a steady dose of progestin into the body which prevents ovulation (the ovary from releasing the egg) and thickens the mucus of the cervix. The thickened mucus prevents the sperm and egg from joining and fertilizing in case the egg is released. Implanon is manufactured by Merck & Co., and was approved by the U.S. Food & Drug Administration (FDA) in 2006.
Benign Intracranial Hypertension & Hormonal Contraceptives
BIH occurs when cerebrospinal fluid (CSF) builds up around the brain, causing symptoms that are similar to those produced by a large brain tumor. The condition may be caused by an increase in CSF production or a decrease in its absorption.
It is unclear why benign intracranial hypertension occurs in many patients. However, certain medications including hormonal contraceptives have been associated with the disorder. Levonorgestrel, a second-generation synthetic hormone contained in the Mirena IUD and other birth control products, was linked to benign intracranial hypertension in 1995.
- Changes in vision
- Vision loss
- Papilledema (swelling of the optic nerve)
- Feeling dizzy or nauseated
- Neck stiffness
- Difficulty walking
- Persistent ringing in the ears (tinnitus)
In patients with benign intracranial hypertension, headache is usually the first symptom: generalized throbbing is the first thing in the morning and last thing at night, and can be relieved by standing (consistent with increased pressure around the brain). These types of headaches are also aggravated by straining, coughing or changing position. In many cases, the headache may be mild, non-specific and have been present for a prolonged period of time (weeks or months).