Presbycusis, deafness of old age

presentation for ent cpd meeting

1. PRESBYCUSIS

2. INTRODUCTION Presbycusis refers to sensorineural hearing impairment in elderly Most common otolaryngologic problem of elderly Involves bilateral high – frequency hearing loss associated with difficulty in speech discrimination and central auditory processing of information Association between advanced age and high tone deafness was first described by Zwaardemaker in 1899

3. Occurs in elderly population that relies on special senses to compensate for other age associated disabilities elderly patients may rely of hearing to overcome limitations of impaired vision as well as slowed reaction time In addition, age associated decline in concentration and memory contribute to difficulty in understanding speech in noisy evn

4. Hearing loss may contribute to the isolation of elderly people by restricting their usage of phone, causing them to forfeit social events such as concerts and social gatherings and amplifying their sense of disability

5. Epidemiology No race, sex differences. Increases with age 25 – 30% of people aged 65 – 75 are estimated to have impaired hearing For people aged 75 or older incidence is thought to be 40 – 50% Westernized countries and primitive civilisations have very different patterns of hearing loss Rosen et al study in Sudanese tribe called mabaans revealed significantly less hearing loss in elderly people than those of urban society

6. Physiologic property Urged to read and revise from Dr C Favara’s presentation titled: Ultrastructure of the cochlea

7. Cochlear duct = coiled duct filled with fluid Ectodermal origin Walls are lined with cells that constitute the membranous labyrinth Constitutes of hair (sensory cells) and auxiliary and supportive cells Membranous labyrinth is surrounded by additional fluid space filled with perilymph and lined by cells of mesodermal origin

8. Role of cochlea is to transduce complex sound waves into electrical activity to transmit to brain via auditory nerve Inner hair cells of organ of corti perform the transduction and initiate the depolarisation of spiral ganglion neurons Outer hair cells are accessory sensory cells that enhance the sensitivity and selectivity of cochlea

9. Basic anatomy of cochlea

10. General organisation of the cochlea The cochlear duct, scala media, is a coiled tube filled with fluid ( endolymph ), in continuity with the vestibular portion of the membraneous labyrinth via the ductus reuniens. It is encased in the bony labyrinth of the petrous portion of the temporal bone. The bony cochlea (outside diameters) is about 1 cm across and 0.5 cm tall. The cochlear duct is surrounded by two additional perilymphatic spaces, the scala vestibuli above and the scala tympani below for all its extent till its apical dead end at the helicotrema. It has a triangular shape in cross-section. Three walls: The floor on which rests the organ of Corti. The superior wall, Reissner membrane. The lateral wall, the stria vascularis supported by the Spiral Ligament.

11. Endolymph vs perilymph Endolymph In scala media Extracellular fluid Ionic composition similar to intracellular fluid High [ K +] , low [Na +] Electric potential of endolymph +80mV = endolymphatic potential perilymph In scala tympani and scala vestibuli Ionic composition similar to CSF or plasma Rich in Na and low in K + Weakly positive electrical potential 5 – 7 mV

12. Only possible ion communication with spaces beyond scala media is through the ion channels situated in the stereo cilia of the sensory hair cells of the organ of corti

13. The stria vascularis generates the end cochlear potential and maintains the ionic composition of the endolymph. The mechanical characteristics of the basilar membrane and its related structures further enhance the frequency selectivity of the auditory transduction mechanism. The tectorial membrane is an extracellular matrix, which provides mass loading on top of the organ of Corti, facilitating deflection of the stereo cilia.

14. Stria vascularis = 3 layers of cells Marginal cells Intermediate cells Basal cells Stria vascularis and spiral ligament are richly supplied by blood vessels

15. Spiral ligament Located between stria vascularis and otic capsule Reaches beyond the limits of stria vascularis and perilymphatic spaces of scala vestibuli and scala tympani Anchors the lateral aspect of the basilar membrane Has prominent capillary bed for the supply and drainage of cochlea

16. Essential structure for maintaining the ionic balance in scala media K+ absorbed via gap junctions K+ ion pumps K+ from scala tympani and organ of corti and reroutes to the basal cells of stria vascularis Implicated in presbycusis ( pathological changes of the fibrocytes of spiral ligament)

17. Base of cochlea is the region where higher sound frequencies are transduced Lower frequencies are transduced at apical end Range of frequencies is tonotopically distributed along the cochlear duct from base to apex

18. the organ of Corti

19. Sensorineural end organ of hearing Contains both sensory and supporting cells Sensory cells are hair cells which have active process in their stereocilliar bundles Receive both afferent and efferent innervation Coupled with tectorial membrane

20. Hair cells are supporting cells are spatially organised in an orderly pattern that extend repetitively for the 2 and half turns of cochlea Every sensory cell is surrounded by four supporting cells Sensory cells have no contact with each other

21. Inner hair cells are true sensory cells, able to send impulses via auditory nerve Outer hair cells enhance the performance of the cochlea’s selectivity and sensitivity The sensory cells do not reach the basilar membrane, only supporting cells do All cells are differentiated, thus no turnover of cells If sensory cells are lost, they are irreplacable

22. Inner hair cells: Pear shaped Central nucleus Apical tight junction No desmosomes At apical surface stereo cilia implanted on cuticular plate Stereo cilia and reticular lamina are in endolymph, rest of cell surrounded by perilymph Base – synaptic connection with afferent nerve terminals

23. Outer hair cells 3 rows on lateral side Cylindrical in shape, nucleus in base Supported by Deiter’s cells Apical surface part of reticular lamina Surrounded by and make tight junction at the upper junction with 4 different deiters cells Hair bundle is W shaped with multiple rows of stereocilia Apical surface endolymph, body on all sides except base by perilymph (space of Nuel)

24. Outer hair cells are stiff and motile Movement modulates distance between reticular lamina and basilar membrane Require presence of protein, prestin in cell membrane to move Prestin can change it’s conformation at microseconds rates dependence of changes in electrical voltage

25. Summary of essential physiology

26. pathophysiology Histologic changes associated with aging occur throughout the auditory system from the hair cells of the cochlea to the auditory cortex in temporal lobe of the brain Elucidation of pathophysiology of presbycusis is still incomplete

27. Crowe and associates Saxen and Gacke and Schuknecht Studied histologic changes in cochlea of human ears with presbycusis Identified 4 sites of aging in cochlea and divided presbycusis into 4 types based on these sites Histologic changes correlated approximately with symptoms and auditory test results

28. Sensory presbycusis Epithelial atrophy with loss of sensory hair cells as well as supporting cells in the organ of corti Originates in basal turn of cochlea and slowly progress towards the apex sharp drop in high frequency threshold, begins after middle age Abrupt downward slope of audiogram begins above speech frequency, speech discrimination is preserved

29. Histologically atrophy may be limited to only the first few millimetres of basal end of cochlea Process is slowly progressive over time ? Due to accumulation of lipofuscin pigment granules at the basal end of cochlea

30. Neural presbycusis Atrophy of nerve cells in the cochlea and central neural pathways Schuknecht estimated that 2100/35000 neurons are lost every decade. Loss begins early in life and may be genetically predetermined Effects not noticeable until old age because PTA not affected until 90% of neurons are gone Atrophy occurs throughout the cochlea Basilar region slightly more predisposed than the remainder of cochlea

31. No precipitous drop in high frequency threshold observed A disproportionally severe decrease in speech discrimination is a clinical correlate of neural presbycusis May be observed before hearing loss is noted because fewer neurons are required to maintain speech thresholds than speech discrimination

32. Metabolic (strial) Results as atrophy of stria vascularis Normally maintains the chemical and bioelectrical balance and metabolic health of cochlea Hearing is represented by a flat hearing curve because entire cochlea is affected Speech discrimination is preserved Process in younger population (30 – 60 years) with slow progression and may be familial

33. Mechanical (i.e. cochlear conductive) Results from thickening and secondary stiffening of the basilar membrane of the cochlea Thickening is more severe in the basal turn of the cochlea where the basilar membrane is narrow Correlates with gradually sloping high frequency sensorineural hearing loss that is slowly progressive Speech discrimination is average for the given PTA

34. Changes associated with presbycusis is rarely found exclusively at one site Development typically involves simultaneous changes at multiple sites Explained by the difficulty of associating specific clinical symptoms or signs with specific anatomical location

35. Large volume of current research is being conducted to determine the exact underlying cause of presbycusis Much of the research focuses on finding underlying genetic abnormalities that may cause, contribute to or predispose to presbycusis

36. Genetic mutation of mitochondrial DNA Reduced perfusion of the cochlea associated with age may contribute to the formation of reactive oxygen metabolites Affect the inner ear neural structures and cause damage to mitochondrial DNA Damaged mitochondrial DNA = reduced oxidative phosphorylation = disruption in ATP production = disruption of K+ channels = neural dysfunction

37. Damaged mitochondrial DNA may lead to anatomic changes of the inner ear Narrowing of the vaso nervorum In the auditory meatus in temporal bone (Dai et al 2006) Greater rates of apoptosis of supporting cells in inner ear (pickles et al 2004) 2 specific deletions mtDNA4834 and mtDNA4977 have been linked to age related hearing loss in rodents Han et al and Dai et al have demonstrated mtDNA4977 deletion with archived human temporal bones from patients with presbycusis

38. Other causes Nutritional and anatomic Berner et al investigated the relation between vitamin B12 and Folate - not significant relationship Martin Villares et al found positive relation ship between high cholesterol levels and hearing loss Statin users had no improvement in rate of presbycusis

39. The Patient…. Presentation varies Patients typically have more difficulty understanding rapidly spoken language, vocabulary that is less familiar or more complex as well as speech within a noisy, distracting environment Localising sound is difficult for patient

40. aetiology Arteriosclerosis Cause diminished perfusion and oxygenation of cochlea Diet and metabolism DM accelerates process of arteriosclerosis Diffuse proliferation and hypertrophy of intimal endothelium which may also interfere with perfusion of cochlea Brainstem neuropathy in DM

41. Accumulated exposure to noise Drug and environmental chemical exposure Genetics stress

42. workup Blood tests for autoimmune Audiology with PTA and speech discrimination Need for additional testing can be determined from the audiometric plus physical examination of the patient

43. treatment Presbycusis is not curable Effects of disease on patients lives can be managed Amplification devices – properly fitted hearing aids Older patients with arthritis and visual difficulties need extra help on learning to use hearing aids Patients using hearing aids may still experience difficulties with speech discrimination in noisy situations

44. Lip reading May help patients with diminished speech discrimination and hearing aid users who have difficulty in noisy evns Assistive listening devices Range from amplification of telephone signal to sound transmitters Cochlear implants Patients with cochlear changes and intact spiral ganglia and central candidates are best candidates

45. Future of treatment… Researchers proposing treatments that address underlying genetic cause Medications that block production of reactive oxygen metabolites (carnitine) may treat presbycusis at molecular level Stem cell transplant into the cochlea to attempt to regenerate sensory cells….