Tinnitus is a medical symptom in which a person perceives a sound, such as ringing or humming, yet it is not a sound that is coming from the environment. Perhaps it is best to consider was tinnitus is not, before tackling what tinnitus is. First, tinnitus is not its own condition or disorder, it is a symptom. When the symptom of tinnitus occurs, it indicates that some other disease process is taking place. Second, the sound heard in tinnitus is not really there; in subjective tinnitus (which the vast majority of people with tinnitus have) there is nothing that is actually making a sound as you would normally think of it. Third, tinnitus is not a hallucination. A hallucination is a psychiatric symptom associated with conditions like schizophrenia. Tinnitus, on the other hand, is a neurological symptom involving the auditory system (hearing system).

Characteristics

The way in which patients with tinnitus experience the unusual sound in their ears differs greatly from person to person. Commonly people will describe the sound as a ringing, so much so that tinnitus is used interchangeably with the phrase “ringing in the ears.” However, the medical symptom can sound just like any nondescript sound: buzzing, whirring, whistling, whooshing, pulsing, or clicking. It can be low pitched, high pitched, or anywhere in between. It can be soft, like ambient background noise or so loud that it becomes difficult to hear actual sounds. The sound that occurs in tinnitus is never a voice or words (which would mean the issue is a hallucination). Finally tinnitus may occur infrequently or be present constantly.

Causes of tinnitus

As mentioned, tinnitus is a symptom, not a distinct medical condition. When people experience this strange sound in the ear(s), it means that there is some other medical issue occurring. There are many different disease and disorders that can cause tinnitus; fortunately none of them are overly severe or imminently life threatening.
Unlike most diseases which stay within a single bodily system, tinnitus can be caused by a problem in one of many different systems. The root cause of tinnitus can be metabolic, neurologic (involving the nervous system, vascular (involving the blood vessels), otologic (involving the ear and hearing system). It can be caused by something as simple as a buildup of earwax to something as complex as fibromyalgia. Certain forms of hearing loss are associated with tinnitus. Also, a number of drugs have been identified as potential causes of the symptom.

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Tinnitus and hearing

Most cases of tinnitus occur in some part of the auditory system. The auditory system includes the ear canal, eardrum, the bones that connect the eardrum to the cochlea, and the nerves that connect the cochlea with the brain (and the auditory cortex). Without drowning in anatomy, it is useful to be aware of each of these structures since it helps frame some of the many causes of tinnitus. The ear canal is home to cerumen (earwax). Too much earwax can lead to strange sounds in the ears and is a common cause of tinnitus. The eardrums and ear bones are next to a variety of blood vessels and other structures that can become inflamed or otherwise abnormal. This too causes phantom noise in the ears. The cochlea is the organ that converts sound waves to nervous tissue impulses so that the brain can detect sound. Along with the vestibular system, these delicate, fantastic structures allow us to hear and maintain balance. However if they do not function properly, several problems can occur.

Hearing loss often goes hand in hand with tinnitus, particularly sensorineural hearing loss. The two main causes of sensorineural hearing loss—namely noise-induced hearing loss and presbyacusis (the loss of hearing that occurs as we age)—are both associated with tinnitus. In sensorineural hearing loss there is some abnormality of the cochlea that leads to decreased hearing, but also to the generation of sounds that are not really there. Not only is the hearing decreased but it is also dysfunctional.

Meniere’s disease is a disease of the vestibular system (the system that helps us maintain balance). Severe cases of Meniere’s disease cause dizziness, nausea, vomiting, a feeling of fullness in the ears and, not surprisingly, tinnitus.

In Meniere’s disease, the ringing can vary to a constant low intensity hum to a sound of deafening proportions during a bout of intense dizziness.The final part of the auditory system, originating at sound wave to brain, is the eighth cranial nerve. It carries electric signals starting in the cochlea to the brain itself. In some people this nerve gets encased and impinged by a benign growth called an acoustic neuroma. This rare growth can interfere with the normal electric signals making the brain perceive noise that is not there. When these growths do occur, they almost always occur on one side of the head, thus tinnitus is only heard on one side as well.

Drugs that cause tinnitus

Several drugs are known to be ototoxic (literally translated as “ear killing”) which means they can cause partial or total deafness. While this is infrequent, especially when the medications are used judiciously, the deafness can be accompanied by tinnitus. In other cases, tinnitus is the only symptom of ototoxic drugs.

Fortunately, some drugs can cause ototoxicity at or near the same dose that is required for a clinical affect. For example, chemotherapeutic agents that are meant to kill cancer cells may also kill the cells in the cochlea as a side effect. More commonly used drugs, like aspirin, are toxic to the cochlea at very high doses. In general, though, more routinely used medications rarely, if ever cause ototoxicity at standard therapeutic doses. Regardless, some people should be particularly careful with ototoxic medicines including the very young and the very old, people with liver and/or kidney disease, women who are pregnant, and loss that are already showing signs of sensorineural hearing loss.

Drugs that may cause hearing loss and/or tinnitus
Aspirin	Nonsteroidal anti-inflammatory drugs (NSAIDs)
Aminoglycosides	Chloramphenicol (Chloromycetin)	Erythromycin
Tetracycline	Vancomycin (Vancocin)	Chloroquine (Aralen)
Bleomycin (Blenoxane)	Cisplatin (Platinol)	Mechlorethamine (Mustargen)
Methotrexate (Rheumatrex)	Vincristine (Oncovin)	Heavy metals: mercury, lead
Bumetanide (Bumex)	Ethacrynic acid (Edecrin)	Furosemide (Lasix)

Other causes

Tinnitus may occur in a variety of neurological diseases. In fact, about 1 in 15 cases of tinnitus have a neurological cause. Multiple sclerosis is a common culprit but so are acquired causes such as skull fracture, closed head injury, and whiplash. Temporomandibular joint disorder (TMJ) can lead to both dizziness and tinnitus. Blood vessels that travel near the eardrum may actually cause a whooshing sound as blood flows through them. While the sound is soft and subtle, it can be heard as tinnitus because it is so close to the eardrum.

Metabolic causes of tinnitus include anemia, hyperlipidemia, thyroid disorder, and vitamin deficiency. Anemia is the condition in which there too few red blood cells circulating in the blood. Hyperlipidemia, better known as high cholesterol, has been linked to tinnitus, but how it causes this symptom is unknown. Either too much or too little thyroid hormone can lead to ringing in the ears. Vitamin B12 and zinc deficiency can cause the symptom as well. People with fibromyalgia sometimes experience tinnitus as one of the many symptoms of that illness.