Hearing loss stems from a variety of sources, including age, genetics, embryologic development, infection and trauma. Congenital hearing loss that is, hearing loss at birth occurs in two to three out of every 1,000 infants. Congenital hearing loss can be caused by a genetic condition or an infection to which the mother or infant was exposed. In addition to these intrauterine and neonatal infections, people of all ages can acquire infections that may lead to hearing loss. Sometimes the infection damages hearing while other times the treatment may be the culprit, such as when ototoxic antibiotics are used (read "The Ototoxic Drug Dilemma: You Live, Hair Cells Die" from the Summer 2010 issue of Hearing Health, online at www.drf.org). Among infections that can cause hearing impairment, meningitis is the most common. At least some degree of hearing loss has been reported in up to 29 percent of bacterial meningitis cases, with a portion of these resulting in profound deafness.
Meningitis is an infection of the lining (the meninges) and fl uid around the brain and spinal column. These infections can spread quickly, leading to signifi cant illness and even death. While meningitis can affect people of all ages, those most affected and negatively impacted by this disease are individuals under the age of 20 years. A recent review (May 2010) by Karen Edmond, Ph.D., found that children younger than fi ve years of age were twice as likely to develop associated chronic conditions compared to older individuals. Elderly people and people with compromised immune systems are also at increased risk of meningitis.
The source of infectious meningitis may be bacterial, viral, fungal or parasitic. Although viral meningitis is the most common, the symptoms related to it are typically less severe and have fewer long-term consequences than symptoms of other forms of the disease. Bacterial meningitis can be very serious and is more likely to have increased morbidity and mortality. The major symptoms of all types of meningitis are fever, headache, stiff neck and altered mental status. Most individuals have at least two of these symptoms when they seek medical attention. Nausea, vomiting, seizures and sensitivity to light (photophobia) are also frequently reported symptoms.
Even though the different forms of meningitis have similar symptoms, treatment differs signifi cantly based on the cause of the infection. For this reason, a thorough patient history and physical examination by a licensed physician becomes critical. The most reliable and benefi cial test for making the diagnosis and determining the treatment is the sampling of the fluid around the brain (cerebrospinal fluid or CSF) by a lumbar puncture (or spinal tap). Using microscopic analysis, CSF is analyzed for opening pressure and the type and presence of organisms. In addition, cell count, glucose and protein concentration are examined. If an organism is identified, special stains and cultures are performed to isolate the specific strain and tailor the medications to the individual infectious agent.
In-patient treatment in a closely monitored setting is often required for cases of meningitis, especially bacterial infections. As the laboratory studies may take some time to provide a fi nal and conclusive answer, broad-spectrum antibiotics, as well as steroids, are often initiated. The addition of steroids to meningitis treatment is believed to alleviate the neurological effects of the disease and prevent long-term consequences, such as blindness and hearing loss. A recent meta-analysis by Van den Bruel et al. published in The Lancet (March 2010) found no signifi cant reduction in mortality or other serious consequences with the addition of steroids; however, the authors did fi nd a signifi cant reduction in hearing loss (24.1 percent hearing loss with steroids compared to 29.5 percent without steroids). Some recent studies have looked at directly injecting steroids into the inner ear to achieve further and more directed hearing preservation in cases of meningitis.
While certain types of meningitis may be directly transmitted from one person to another, meningitis often stems from an infection elsewhere in the body, such as the lungs, ears, sinuses or other parts of the body. Fortunately, the treatment for the related meningitis also treats the primary infection and additional therapy is not required. Occasionally, if the source is a severe ear infection, the placement of an ear tube with application of ear drops is often sufficient additional management.
Modern-day advances in vaccines have had an enormous impact on the incidence and prevalence of meningitis. According to the Centers for Disease Control and Prevention, before the Haemophilus infl uenzae type B (H flu) vaccine, known as Hib, was introduced in the mid-1980s and then entered widespread use in the 1990s, H flu was the leading cause of bacterial meningitis. Thanks to the routine immunization of children with the Hib vaccine, H fl u no longer contributes as significantly to the number of meningitis cases, and the overall number of cases of meningitis has been reduced. Vaccines against the other two main causes of bacterial meningitis, Streptococcus pneumoniae and Neisseria meningitidis, are also available and routinely used in select groups that are at higher risk.
Treatment of Associated Hearing Loss
Despite prompt evaluation and treatment, serious chronic health conditions often result from meningitis. Blindness, deafness, mental retardation and even death can occur. Hearing loss is the most common of these consequences, particularly in cases of meningitis caused by H flu. The national incidence of hearing impairment caused by meningitis was 3.2 percent, according to the 2005-2006 Annual Survey of Deaf and Hard of Hearing Children and Youth by the Gallaudet Research Institute. While it was the leading cause of post-natal hearing loss less than a decade ago, it is now the second most common cause. In addition to hearing loss, other earrelated functions can be affected by meningitis, resulting in balance problems and tinnitus (an abnormal subjective ringing sound experienced in the ear).
Mild hearing loss due to meningitis may be effectively treated with hearing aids and those who develop severe to profound hearing loss may benefi t from cochlear implantation. The cause of significant hearing loss related to meningitis is often unique, therefore, results and outcomes for cochlear implantation are optimal
when the procedure is done without delay. While some cases of meningitic hearing loss are due to death of the nerve endings (hair cells) in the hearing organ (cochlea), bacterial meningitis can also lead to a severe disorder called labyrinthitis ossifi cans. This is a progressive obliteration of the structure of the cochlea that can make cochlear implantation much more difficult and even result in only partial electrode array insertion, reducing the implant's capacity to achieve good hearing outcomes.
Daniel Philippon, D.M.D., M.D., and his colleagues in Quebec recently published a scholarly article regarding their 20-year experience with post-meningitic cochlear implants. Their conclusion was that rapid obliteration of the cochlea can occur and that recovery from profound deafness is very rare. They support early assessment and intervention to maximize hearing outcomes, as opposed to a watchful, waiting approach. More intensive investigation to identify and treat these patients is warranted since earlier intervention may improve implant effi cacy.
Meningitis continues to be a life-threatening disease and a menace to hearing health. However, medical and technological advances have provided us with some critical protections and interventions, with vaccinations and cochlear implants being key among them. But most importantly, a clear understanding of the clinical presentation and proper treatment of meningitis and associated chronic conditions is crucial if we are to continue to make headway in the prevention and treatment of this devastating disease.
Larry D. Hartzell, M.D., is an instructor in the Department of OtolaryngologyHead and Neck Surgery, University of Arkansas for Medical Sciences, and a Pediatric Otolaryngology Fellow, Arkansas Children's Hospital, Little Rock, Ark.
John L. Dornhoffer, M.D., is a professor, vice-chair and director of the Division of Neurotology, Department of OtolaryngologyHead and Neck Surgery, University of Arkansas for Medical Sciences. Dornhoffer is also vicepresident of Deafness Research Foundation's Centurions.
