REPORT FORMName: _________________________________ Condition:Histology
The inner ear consists of a membranous “labyrinth” encased in an occeous labyrinth. The vestibule and semicircular canal are concerned with vestibular function (balance); cochlea is concerned with hearing. The cochlea is a coiled tube. The cochlea coils up from its base. It is coiled around the modiolus. The Reissner’s membrane and the basilar membrane divide the cochlea longitudinally into three scalae. If you cut the cochlear tube cross sectionally, you’d see Scala vestibuli on top, scala tympani on the bottom. Scala media is a triangular duct in the middle. The side of the duct where the nerve fibres exit is the “inner” or “modiolar” side of the duct. The opposite side is the “outer” side. In the organ of corti, the scala media is triangular in shape. It is formed by Reissner’s membrane, basilar membrane and the structure called the stria vascularis. The organ of corti rests on the basilar membrane within scala media. There are two types of cells in the organ of corti, and are called support cells and hair cells. The hair cells are the “receptor” cells, and are responsible for transductance of sound. Support cells such as Deiter’s cells have supportive function, and they support hair cells. The tops of the hair cells and pillar cells form the reticular lamina. This lamina isolates the hair cells’ stereocilia from their cell bodies. The tectorial membrane is loosely coupled to the reticular lamina,
According to , the cause of AIED is thought to be related to either antibodies or immune cells that cause damage to the inner ear. Here is a list of theories about possible pathogenesis. Bystander damage: damage to the inner is causes Cytokines to be released which lead to immune reaction. Cross-reactions: Antibodies or the rouge T-cells cause accidental damage because ear share common antigen with viruses, bacteria or other harmful substances. Intolerance: In this case body may not know about all the inner ear antigens, and it may attack them upon their release thinking they are foreign substances. And finally, the Genetic predisposition is also suspected to play a role.
The diagnosis of AIED is not easy, and an otolaryngologists trained in autoimmune diseases are best trained diagnose it. The best test for its diagnosis is 68-kd antigen, are expensive and rare. The tests are not as accurate we one would like, and can give false-positive and false-negative test. The tests commonly used are : audiometry, ABR, rotatory chair test and ECOG. In addition, the following blood tests for generalized autoimmune diseases are also useful: ANA, ESR, rheumatoid factors etc.
Pathology/Pathophysiology:
According to , the diagnosis of AIED maybe be overlooked due to lack of specific diagnostic tests. However, it can be clinically diagnosed as a rapidly progressing, at times fluctuating bilateral sensorineural loss of hearing. This progresses for a period of weeks to a few months. To make differential diagnosis, one can observe the progression of this disease. It is too rapid to suggest diagnosis of presbycusis and too slow to suggest diagnosis of sudden SNHL. About 50% of patients present vestibular symptoms such as, generalized imbalance, ataxia, postural vertigo and episodic vertigo. Initially one ear is affected, but ultimately bilateral hearing loss occurs in patients with symmetric or asymmetric thresholds. About 25 to 50% patients report having tinnitus and aural fullness that can fluctuate. About 15-30% of patients have coexisting systemic autoimmune disease.
Further, the onset of hearing loss in this disease is rather rapid as compared to other diseases that cause auditory dysfunction. The progression to hearing loss occurs over the course of weeks to months. Patients have problems with both hearing acuity and word discrimination. They may find following conversations in noisy environments particularly challenging. Also, vestibular problems that result from cochlear damage can be as challenging as the auditory dysfunction. Pharmacology:According to , the glucocorticoids are potent inhibitors of inflammatory processes, and their effect is mediated through two mechanisms. First, through direct binding of glucocorticoid/glucocoriticoid receptor complex to glucocorticoid responsive elements, in the promoter region of genes. The second mechanism is by interaction of this complex with the other transcription factors, in particular activating protein-1 or nuclear factor-kappaB. They also inhibit molecules associated with inflammation such as cytokines, chemokines, arachidonic acid metabolites, and adhesion molecule.
According to , the steroids are the first choice of drugs for the treatment of AIED. In case of classic bilateral disease, a triad of steroids such as prednisolone or dexamethasone for four weeks can be tried. This regimen is inexpensive and effective, but has side-effects as they effectively reduce the body immunity. Cytotoxic agents such as Cyclophosphamide or Methotrexate can be tried for long term, especially those who respond to steroids. These are basically anti-cancer agents that act by killing unwanted cells. Other drugs such as enoxaparin and rituximab can be used.
Bibliography
Agrawal, Y., & Francis, H. W. (2010). Immune-Mediated Inner Ear Disease. In Y. Agrawal, & H. W. Francis, A Clinician's Pearls and Myths in Rheumatology (pp. 385 - 392). London: Springer.
Autoimmune Inner Ear Disease: What is autoimmunity? How is it connected to vestibular disorders? (n.d.). Retrieved from Vestibular Disorder Association: http://vestibular.org/autoimmune-inner-ear-disease-aied
Bovo, R., Aimoni, C., & Martini, A. (2006). Immune-mediated inner ear disease. Acta Otolaryngol, 1012 - 21.
Hain, T. C. (2012, 10). Autoimmune Inner Ear Disease (AIED). Retrieved from American Hearing Research Foundation: http://american-hearing.org/disorders/autoimmune-inner-ear-disease-aied/
Mathur, N. N. (n.d.). Autoimmune Disease of the Inner Ear . Retrieved from Medscape: http://emedicine.medscape.com/article/857511-overview
Ross, M. H., & Pawlina, W. (2010). Ear. In Histology: A Text and Atlas. Lippincott Williams & Wilkins. Retrieved from https://www.inkling.com/read/histology-michael-ross-and-wojciech-pawlina-6th/chapter-25/internal-ear
van der Velden, V. H. (1998). Glucocorticoids: mechanisms of action and anti-inflammatory potential in asthma. Mediators Inflamm., 229-267.
