WHAT ARE HEARING DISORDERS?
Developmental hearing disorders (DHDs) are conditions that affect the auditory system from birth or early childhood, resulting in hearing impairments. These disorders may arise from genetic mutations, congenital infections, neurodevelopmental abnormalities, or environmental factors that affect sound processing.
WHAT ARE THE TYPES OF HEARING DISORDERS (HD)?
NRS can be classified as follows:
Congenital hearing loss (genetic or non-genetic)
Auditory Neuropathy Spectrum Disorder (ANSD) is a dysfunction of the auditory nerve with intact cochlea function.
Central Auditory Processing Disorder (CAPD) is a disorder in which the brain has difficulty processing sounds despite normal hearing.
Delayed maturation of the auditory system - a temporary delay in the development of hearing
Sensorineural hearing loss (SNHL) is a disorder of the inner ear or auditory nerve.
Conductive hearing loss is a disorder of sound conduction through the outer or middle ear.
WHEN DO HEARING PROBLEMS BEGIN?
NCDs may occur in utero, at birth, or in early childhood. Some are detected by newborn audiological screening, while others become apparent later in life due to progressive or delayed onset of auditory dysfunction.
CLINICAL MANIFESTATIONS OF HEARING DISORDERS
Delayed speech and language development
Weak response to auditory stimuli
Difficulty understanding speech in noisy environments
Frequent repeating of questions
Distortion of perception of sounds and words
Difficulties in educational education
Difficulties in social communication
WHAT CHANGES IN THE BRAIN PRECAUTION HEARING DISORDERS?
Developmental anomalies of the auditory cortex (reduced volume, connectivity disorders)
Delayed myelination of the auditory pathways
Decreased synapse density in the brainstem
Cortical reorganization – in severe hearing loss, the visual and somatosensory cortices can partially compensate for lost auditory functions
Changes in activity in the superior temporal gyrus that affect speech perception
WHAT SPECIFIC AREAS OF THE BRAIN AND PERIPHERAL NERVOUS SYSTEM ARE AFFECTED IN HEARING DISORDERS?
Genetic mutations are the main cause
Congenital infections (TORCH: CMV, toxoplasmosis, rubella, syphilis, herpes, Zika virus, etc.)
Perinatal hypoxia
Prematurity and low birth weight
Ototoxic drugs (aminoglycosides, loop diuretics, chemotherapy)
Autoimmune diseases of the inner ear
Neurodevelopmental disorders (autism, ADHD, dyslexia are associated with CAPD)
WHAT ARE THE MAJOR GENETIC MUTATIONS ASSOCIATED WITH HEARING DISORDERS?
GJB2 (connexin 26) mutation is the most common cause of congenital hearing loss
SLC26A4 (Pendred syndrome) - hearing loss with thyroid dysfunction
OTOF – auditory neuropathy
MITF, PAX3 (Waardenburg syndrome) - a combination of hearing loss with pigmentation anomalies
TMC1 - progressive hearing loss
THE ROLE OF INFLAMMATION AND NEUROINFLAMMATORY IN HEARING DISORDERS
Neuroinflammation disrupts auditory signal transmission
Microglia activation in the auditory brainstem
Cytokines (IL-1β, TNF-α, IL-6) impair neuronal functions
THE ROLE OF CHRONIC AND LATENT INFECTIONS IN HEARING DISORDERS
CMV is the leading cause of non-genetic congenital hearing loss.
Chronic infections (herpes viruses, toxoplasmosis, syphilis) can affect the auditory system
Recurrent middle ear infections can lead to conductive hearing loss
HEARING DISORDERS AND IMMUNE SYSTEM DYSREGULATION
Autoimmune reactions against proteins of the inner ear
Cytokine imbalance (IL-1β, TNF-α, IFN-γ)
The influence of maternal immune response on fetal auditory development
HEARING DISORDERS AND THE POSSIBLE ROLE OF THE MICROBIOME
Dysbacteriosis affects neuroinflammation, affecting the auditory system
Gut-Brain Axis Dysfunction
Association of H. pylori infection with chronic otitis
HEARING DISORDERS AND ENDOCRINE SYSTEM DYSREGULATION
Hypothyroidism (including Pendred syndrome) is a common cause of hearing loss
Type 1 and 2 Diabetes – Risk of Progressive Hearing Loss
Stress hormones may alter auditory processing
HEARING AND METABOLIC DISORDERS
Mitochondrial dysfunction (m.1555A>G) – aminoglycoside sensitivity
Hypoxia-induced metabolic stress
Lipid metabolism disorder (Niemann-Pick disease, Gaucher disease)
OFFICIAL METHODS OF TREATMENT OF HEARING DISORDERS
Hearing aids and cochlear implants
Audio Verbal Therapy (AVT)
Speech therapy assistance
Hearing enhancement devices (FM systems, bone-anchored hearing aids)
PROSPECTS FOR ANTI-INFLAMMATORY AND ANTI-INFECTIOUS THERAPY
Corticosteroids for acute hearing loss
Antiviral drugs (tests of valganciclovir in CMV infection)
Probiotics to improve hearing
Antibiotics for chronic ear infections
MORE INFORMATION ABOUT HEARING PROBLEMS
TORCH infections and hearing disorders including sensorineural hearing loss, hyperacusis, misophonia and phonophobia
TORCH infections (Toxoplasmosis, Other, Rubella, Cytomegalovirus, Herpes simplex virus) are a significant cause of congenital anomalies, including hearing impairment.
Sensorineural hearing loss and TORCH infections
CMV (cytomegalovirus) infection is the most common neurogenetic cause of sensorineural hearing loss (SNHL) in children. Studies show that approximately 12.6% of children with congenital CMV have hearing loss, with symptomatic cases more likely to have bilateral and severe hearing loss. This hearing loss may be present from birth or develop later, often being progressive or fluctuating.
Goderis J, De Leenheer E, Smets K, Van Hoecke H, Keymeulen A, Dhooge I. Hearing loss and congenital CMV infection: a systematic review. Pediatrics. 2014 Nov;134(5):972-82. doi: 10.1542/peds.2014-1173. PMID: 25349318.
Cochlear implantation has emerged as a promising treatment option for children with profound SNHL caused by TORCH infections. A review of 26 studies assessed the efficacy of cochlear implants in this patient group and found that although implantation can significantly improve auditory perception, the results are variable, highlighting the need for an individualized approach to treatment.
Cochlear implant performance in children deafened by torch infection: Scoping review. https://pubs.aip.org/aip/acp/article-abstract/3080/1/110001/3269617/Cochlear-implant-performance-in-children
HYPERACUSIS, MYSOPHONIA AND PHONOPHOBIA
In addition to hearing loss, some patients experience problems with sound perception:
Hyperacusis is an increased sensitivity to common sounds, causing discomfort or even pain with sounds that are usually perceived as normal. This condition is often associated with tinnitus (ringing in the ears), autism spectrum disorders, and post-traumatic stress disorder (PTSD).
Misophonia is a strong emotional reaction (anger, anxiety) to certain sounds, especially those associated with human activity (chewing, breathing, etc.). The exact causes remain unclear, but it is thought to be related to abnormal activation of the central auditory system and its connections to the limbic system.
Phonophobia is a fear of certain sounds that causes anxiety and avoidance behavior. Unlike hyperacusis, which is related to the intensity of sound, phonophobia is more related to an emotional response and fear of sounds.
Treatment for these conditions often involves counseling and sound therapy. For example, Tinnitus Retraining Therapy (TRT) is adapted to gradually reduce negative reactions to certain sounds. However, the effectiveness of treatment varies, and further research is needed to develop standard therapeutic approaches.