Tinnitus

# Overview
Tinnitus is derived from the Latin word tinnire, meaning to ring. Tinnitus can be classified as subjective and objective.  This classification not only explains the underlying etiology but also directs the management of tinnitus. In the normal functioning auditory pathway, there is ordered tonotopic frequency mapping from the cochlea to the auditory cortex via midbrain.  Conditions associated with cochlear damage result in altered tonotopic organization and ultimately tinnitus. The pathophysiology of tinnitus can be explained by the tinnitus model. Common causes of tinnitus include Ototoxicity, Presbycusis, noise induced hearing loss, late onset congenital hearing loss, meniere's disease,  and Loop diuretics. The incidence rate of tinnitus increases with age and is more prevalent in older people. Tinnitus is more prevalent in men compared to women and smokers compared to non-smokers. If left untreated, patients may progress to functional impairment, insomnia, anxiety, and depression. TSI is used to rank the patient's based upon their severity. The score ranges from 0-45. Symptoms and history include sounds such as ringing, buzzing, pulsatile, roaring and humming and progressive hearing loss.  An extensive neurological examination may rule out underlying brainstem damage or hearing loss. The Weber and Rinne test are done to establish sensorineural or conductive hearing loss. They are usually abnormal.  MRI with contrast is followed by CT/CTA and ultimately interventional angiography, if needed. Initial audiometric tests are done to identify asymmetries between the ears and to locate the site of abnormality such as middle ear, cochlea, and brainstem.  These tests include: pure-tone audiogram, tympanometry, auditory reflex testing, determination of speech discrimination abilities, otoacoustic emissions testing and auditory brainstem response testing (ABR).  Tinnitus is a symptom and not a disease itself.  It is a chronic condition that can be managed by treating the underlying etiology. The treatment of tinnitus is usually directed towards improvement in the quality of life by decreasing awareness or desensitizing towards tinnitus.  It is usually achieved by identifying the underlying pathology or the associated disease. It is recommended to treat underlying insomnia and depression (Grade 1B). Cochlear implants may be considered for tinnitus associated with severe sensorineural hearing loss. Other therapies include: tinnitus retraining therapy (TRT) (Grade 1C), biofeedback (Grade 2C), and  cognitive behavioral therapy (CBT) as an adjunct to TRT (Grade 2C). Acupuncture and electrical stimulation are considered equally effective as placebo, no significant role established so far.

# Historical Perspective
- In the early 19th century, Frenchman and Jean Marie Gaspard Itard introduced the concept of masking.  They were the first ones to differentiate between subjective and objective tinnitus.
- Later in the 19th Century, with the introduction of germ theory and anesthesia, surgical therapy such as incudectomy was established.
- Tinnitus is derived from the Latin word tinnire, meaning to ring.

# Classification
Tinnitus can be classified as subjective and objective.  This classification not only explains the underlying etiology but also directs the management of tinnitus.

## Subjective tinnitus:
- It is only experienced by the affected individual in the absence of any auditory stimulation
- More common, usually described as continuous ringing, high pitch sound

## Objective tinnitus:
- It is experienced not only by the affected individual but also by anyone else
- Relative rare, usually described as intermittent venous hum, low pitch sound
- It has an underlying vascular (abnormality of the carotid artery, jugular bulb or jugular vein) or muscular etiology (degenerative conditions such as amyotrophic lateral sclerosis) and usually caused by sound produced in ear, head or neck.

# Pathophysiology
In the normal functioning auditory pathway, there is ordered tonotopic frequency mapping from the cochlea to the auditory cortex via midbrain.  Conditions associated with cochlear damage result in altered tonotopic organization and ultimately tinnitus. The pathophysiology of tinnitus can be explained by the tinnitus model.

### Lesion projection zone (LPZ):
This zone is defined as the area in the auditory cortex that represents the damaged cochlear input.  The neurons in the LPZ zone show 2 main changes:
- Accelerated spontaneous firing rate
- Increased representation of neurons that represent the damaged cochlear region also known as lesion edge frequencies in the LPZ

## Tinnitus model:
This model explains 2 major phenomena in the auditory cortex caused by lack of sensory peripheral auditory input (cochlea)
- Hyperactivity in the lesion projections zone (LPZ)
- Increased cortical representation of the lesion-edge frequencies in the LPZ

# Causes of subjective tinnitus

### Sensorineural hearing loss:
- Ototoxicity
- Presbycusis
- Noise induced hearing loss
- Late onset congenital hearing loss
- Idiopathic

### Cochlear injury:
- Meniere's disease
- Loop diuretics
- Platinum based chemotherapy
- Antibiotics
- Salicylate
- Trauma

### Vascular causes:
- Systemic hypertension
- Sickle cell anemia
- Small vessel disease
- Hypercholesterolemia
- Hypercoagulable state
- Diabetic vasculopathy

### CNS causes:
- Pseudotumor cerebri
- Stroke
- Vascular malformations
- Tumor
- Sarcoid
- Multiple sclerosis

### Infections:
- Rubella
- Cytomegalovirus
- Chronic otitis media
- Neurosyphilis
- Measles
- Lyme disease
- Meningitis

### Bone disease:
- Otosclerosis
- Fibrous dysplasia
- Osteogenesis imperfecta
- Paget's disease

### Metabolic disorders:
- Hyperparathyroidism
- Chronic renal failure
- Diabetes mellitus
- Thyroid disease

### Autoimmune diseases:
- Autoimmune inner ear disease
- SLE
- Rheumatoid arthritis

### Medications:
- ACE inhibitors
- Antimalarial medications
- Aminoglycosides
- Dapsone
- Doxazosin
- Calcium channel blockers
- Benzodiazepines
- Cisplatin
- Clarithromycin
- COX-2 inhibitors
- Loop diuretics
- Tricyclic antidepressant

# Differential Diagnosis of Tinnitus
ABBREVIATIONS
VZV= Varicella zoster virus, MRI= Magnetic resonance imaging, ESR= Erythrocyte sedimentation rate, EEG= Electroencephalogram, CSF= Cerebrospinal fluid, GPe= Globus pallidus externa, ICHD=  International Classification of Headache Disorders

# Epidemiology and Demographics
- Tinnitus affects 10 to 15% of the population.
- 85% of the population presenting with ear symptoms/disorders report tinnitus as an associated symptom.
- The incidence rate of tinnitus increases with age and is more prevalent in older people.
- Tinnitus is more prevalent in men compared to women and smokers compared to non-smokers.

# Risk Factors
Common risk factors of tinnitus include
- Age
- Sensorineural hearing loss
- Loud noise exposure
- Vestibular schwannoma
- Ototoxic medication
- History of anxiety and depression
- History of head trauma
- History of multiple sclerosis

# Natural History, Complications and Prognosis
- Early clinical features may include ear fullness, huming or ringing sensations in the ear
- If left untreated, patients may progress to functional impairment, insomnia, anxiety, and depression.

# Diagnosis

## Diagnostic criteria:

### Tinnitus severity index (TSI)
- TSI is used to rank the patient's based upon their severity
- The score ranges from 0-45

### Tinnitus handicap questionnaire:
- This questionnaire includes 27 questions and is used to estimate the social, physical and emotional handicap severity

### Tinnitus handicap inventory:
- This questionnaire has 4 categories to classify severity
- None, mild,  moderate, and severe.

## History and Symptoms:
- Sounds such as ringing, buzzing, pulsatile, roaring and humming
- Progressive hearing loss
- Recent exposure to excessive or loud noise or head trauma
- Poor hygiene leading to cerumen impaction
- Ear pain
- History of certain medication exposure

## Physical Examination:
- The ear examination may show signs of cerumen impaction, underlying infection or tympanic membrane perforation.
- Auscultation of neck, orbits and periauricular areas as helpful in establishing the diagnosis of vascular causes
- An extensive neurological examination may rule out underlying brainstem damage or hearing loss
- The Weber and Rinne test are done to establish sensorineural or conductive hearing loss. They are usually abnormal.

## Laboratory Findings:
- There are no specific lab findings associated with tinnitis.

## Imaging:
- MRA and CTA are the gold standard diagnostic tests for arteriovenous fistula related tinnitus.
- MRI with contrast is the initial preferred diagnostic test of choice for suspected vascular tinnitus.
- MRI with contrast is followed by CT/CTA and ultimately interventional angiography, if needed.

## Other Diagnostic Testing:
- Initial audiometric tests are done to identify asymmetries between the ears and to locate the site of abnormality such as middle ear, cochlea, and brainstem.  These tests include:
Pure-tone audiogram
Tympanometry
Auditory reflex testing
Determination of speech discrimination abilities
Otoacoustic emissions testing
Auditory brainstem response testing (ABR)
- Pure-tone audiogram
- Tympanometry
- Auditory reflex testing
- Determination of speech discrimination abilities
- Otoacoustic emissions testing
- Auditory brainstem response testing (ABR)

# Treatment
- Tinnitus is a symptom and not a disease itself.  It is a chronic condition that can be managed by treating the underlying etiology.
- The treatment of tinnitus is usually directed towards improvement in the quality of life by decreasing awareness or desensitizing towards tinnitus.  It is usually achieved by identifying the underlying pathology or the associated disease.
- It is recommended to treat underlying insomnia and depression. (Grade 1B)

## Medical Therapy
Following medications have minimal to modest role in relieving tinnitus.
- Misoprostol
- Lidocaine (intratympanic or intravenous)
- Benzodiazepine (alprazolam)
- Steroids such as dexamethasone (intratympanic)
- Carbamazepine
Following medications have been studied for tinnitus but are not found to be effective and have no role in the treatment of tinnitus
- Anticonvulsants
- Melatonin
- Ginkgo biloba
- Niacin

## Surgery
- Cochlear implants may be considered for tinnitus associated with severe sensorineural hearing loss.

## Other therapies:
- Tinnitus retraining therapy (TRT) (Grade 1C)
- Biofeedback (Grade 2C)
- Cognitive behavioral therapy (CBT) as  an adjunct to TRT (Grade 2C)
- Acupuncture and electrical stimulation are considered equally effective as placebo, no significant role established so far.

## Prevention
- Tinnitus may be been prevented by limiting the exposure to loud noise.