Severe hearing impairment means partial or full loss of the ability to perceive sound. Ototoxic drugs, head injuries, sudden pressure changes, and exposure to loud noises are causes of hearing loss which are, to some degree, preventable. Other causes of severe hearing impairment such as infection, presbycus, congenital conditions, and hereditary diseases are typically unavoidable.
Ototoxic drugs, with the prefix “oto” meaning ear, are medications which cause temporary or permanent hearing loss at normal doses or overdoses. Some types of antibiotics, chemotherapy drugs, loop diuretics, and non-steroidal anti-inflammatory medications are ototoxic drugs. The mechanism which causes the hearing loss is not known, but these types of drugs may damage the receptors or hair cells of the ear. Benefits of these drugs must far outweigh the dangers of auditory damage before they are prescribed.
Head injury, sudden pressure changes, and exposure to loud noises can all result in severe hearing impairment. A head injury can result in hearing loss by bursting the ear drum, damaging the ossicles, or when brain swelling following the trauma, damages the auditory part of the brain. Pressure changes, such as while scuba diving or flying in an airplane, can damage hearing by rupturing the eardrum. Loud music or machinery can damage irreplaceable ear hair cells, resulting in permanent hearing loss.
Ear infections typically cause fluid to accumulate in the middle ear, preventing sound from penetrating the inner ear, and causing muted or lost hearing. This type of hearing loss is usually temporary, but if the infection is severe and left untreated, the fluid buildup can cause permanent hearing loss. Other infections which can cause severe hearing loss are bacterial meningitis, Lyme disease, mumps, and herpes.
Presbycusis, or age related hearing loss, can produce gradual but ultimately severe hearing impairment. The culprit is typically damage done to ear hair cells over a lifetime of exposure to loud noises. Hair cells do not regenerate, so eventually enough hair cells are lost to impact hearing.
Congenital conditions which produce severe hearing impairment are premature birth, oxygen deprivation, severe jaundice, and rubella or syphilis during pregnancy. The auditory system finishes developing towards the end of gestation, so hearing loss is one of the many problems which may occur in premature babies. Oxygen deprivation, during birth or immediately following birth, may produce hearing loss when the auditory portion of the brain is oxygen starved and irreparably damaged. Contracting rubella during pregnancy will occasionally result in hearing loss in the fetus, and untreated congenital syphilis and jaundice can also result in progressive hearing loss.
Common hereditary causes of severe hearing impairment are osteogenesis imperfect, Hurler, and Hunter syndromes. Osteogenesis imperfect is a condition characterized by extremely feeble bones, and deafness occurs in about half of the people afflicted by this disease. Hurler and Hunter syndromes are both caused by the buildup of mucopolysaccharides in the body due to a deficiency of specific enzymes. In both syndromes, severe hearing impairment is most likely due to a build-up of fluid in the middle ear, preventing the amplification of sound.
