What is Amyloidosis?

Amyloidosis is a rare group of disorders characterised by the abnormal deposition of misfolded proteins, known as amyloid fibrils, in tissues and organs throughout the body. These insoluble protein deposits can accumulate in the kidneys, heart, liver, nerves, and other structures, progressively disrupting normal organ function. The condition may be systemic, affecting multiple organ systems, or localised to a single tissue site. When amyloid deposits form within the delicate structures of the auditory and vestibular system, the consequences for hearing and balance can be significant.

Amyloidosis and the Inner Ear

The inner ear is a highly specialised sensory organ responsible for both hearing and balance. It contains the cochlea, which converts sound vibrations into neural signals, and the vestibular labyrinth, which detects head position and movement. Amyloid deposits can infiltrate these structures directly or impair their blood supply through involvement of small blood vessels. Deposition may occur within the spiral ganglion, the auditory nerve, the stria vascularis, or the vestibular neuroepithelium, leading to a range of otological symptoms.

Hearing Loss

Sensorineural hearing loss is a common manifestation of inner ear amyloidosis. Damage to the hair cells of the cochlea or to the auditory nerve fibres can result in reduced hearing acuity, particularly at high frequencies. Patients may also experience sudden hearing loss, which can occur when amyloid deposition compromises the vascular supply to the cochlea. The severity of hearing impairment is often progressive, and bilateral involvement is frequently observed.

Vestibular Dysfunction and Dizziness

Amyloidosis can also affect the vestibular system, leading to dizziness, vertigo, and imbalance. Amyloid deposits within the semicircular canals, otolith organs, or vestibular nerve may impair the brain's ability to sense motion and spatial orientation. Patients may describe a sensation of unsteadiness, episodes of spinning vertigo, or persistent gait disturbance. These symptoms can be particularly disabling and may precede the diagnosis of the underlying systemic disease.

Tinnitus

Tinnitus, or the perception of noise in the absence of an external source, is another symptom reported by individuals with amyloidosis affecting the inner ear. The exact mechanism is uncertain, but it is thought to arise from aberrant neural activity in the auditory pathway caused by damage to the cochlea or auditory nerve. Tinnitus may be intermittent or constant and can significantly affect quality of life.

Diagnosis

Diagnosing inner ear involvement in amyloidosis requires a comprehensive evaluation by an otolaryngologist and a neurologist. Audiometry and tympanometry are used to characterise the type and degree of hearing loss. Vestibular testing, including videonystagmography and posturography, can assess balance function. Imaging studies such as magnetic resonance imaging may reveal abnormalities of the inner ear or the internal auditory canal. Definitive diagnosis of amyloidosis itself requires tissue biopsy with Congo red staining, which demonstrates the characteristic apple-green birefringence under polarised light. In cases of suspected hereditary amyloidosis, genetic testing may be helpful.

Treatment and Management

There is no specific cure for amyloidosis, and treatment focuses on managing the underlying disorder and alleviating symptoms. Options depend on the type of amyloidosis and may include chemotherapy, immunomodulatory agents, or targeted therapies to reduce amyloid production. In hereditary transthyretin amyloidosis, liver transplantation or gene-silencing drugs may be considered. For inner ear symptoms, hearing aids and cochlear implants can improve auditory function in appropriate candidates. Vestibular rehabilitation therapy may help patients adapt to balance disturbances. Regular audiological monitoring is recommended to track progression and adjust rehabilitation strategies.

Prognosis

The prognosis for individuals with amyloidosis and inner ear involvement varies widely depending on the extent of systemic disease and the specific amyloid type. Early recognition of hearing loss and vestibular symptoms may lead to earlier diagnosis of amyloidosis, allowing for timely intervention. Although inner ear manifestations are rarely life-threatening on their own, they serve as important markers of a condition that can affect multiple vital organs. Multidisciplinary care is essential to address the complex needs of these patients.

Conclusion

Amyloidosis can profoundly affect the inner ear, producing sensorineural hearing loss, dizziness, tinnitus, and balance impairment. An awareness of this association is important for clinicians evaluating patients with unexplained audiovestibular symptoms, particularly when systemic signs of amyloid deposition are present. Continued research into the mechanisms of amyloid toxicity within the inner ear may ultimately lead to more effective treatments for this challenging condition.