Cronificación de perforación timpánica en ratas con mitomicina C

Resumo

ABSTRACT Chronic otitis media in humans is an affectation of the middle ear that occurs in different clinical forms, the most frequent of them is eardrum perforations. This entity is an integral part of the tympanic membrane and its treatment is a procedure called myringoplasty. Another type of chronic otitis media is otitis media with effusion which is described as the accumulation of mucus in the middle ear. Treatment consists on draining the mucus and placing a transtympanic prosthesis to hold the previously made drilling (myringotomy) open. The great variety of materials used in the myringoplasty is evidence that the results are unsatisfactory and therefore research into new alternatives for biological scaffolds that may promote healing, such as amniotic membrane remains open. For this, we need an animal model with chronicity of perforated eardrum. In our review of the previous research, we have found studies that could get the chronicity of the tympanic perforations by conducting laser myringotomy and applying hydrocortisone or mitomycin C, the latter being a cytostatic that has been used to delay healing various diseases in ophthalmology and otolaryngology. Due to the fact that a laser is not routinely available in research laboratories, it was decided to develop a model of chronic tympanic perforation by incisional myringotomy with mitomycin C. We performed a prospective analytical trial with 34 male Sprague Dawley rats with an average weight of 331.4 grams, divided into three groups: A, B and C. Group A consisted of 10 rats which have undergone a myringotomy with amputation of the handle of the hammer and subsequent application of mitomycin C (0.4 mg / ml) to the left ears (subgroup A1) and saline solution (0.9%) to the right ears (subgroup A2). The B group were 12 rats divided into 4 subgroups, two of them (B1 and B2) formed for 10 ears each, which were applied mitomycin C before myringotomies without amputation of the handles of the hammers (B1) and with amputation (B2). The remaining 4 ears of this group were treated with saline prior to myringotomy , two of them without amputation of the handles of the hammers (B3) and the other two with amputation (B4). The C group of 12 rats was structured like the B group, but dexamethasone (4 mg / ml) was added in the four first reviews of the C1 and C2 subgroups and saline in the same revisions of the C3 and C4 subgroups. The results show an average duration of the drillings in the ears treated with saline of 8.3 days. Ears treated with mitomycin C had an average duration drillings of 18.6 days in group A, group B 15.1 days and 112.7 days group C. There was no significant difference between performing myringotomy obtained with or without amputation of the hammer handle, nor was there when appliying mitomycin C before or after myringotomy. But there was a significant difference between those drillings treated with mitomycin C and those treated with saline and also between the drillings treated exclusively with mitomycin C and those treated with mitomycin C together with dexamethasone. As the chronicity of the tympanic perforations in animals is set from 8 weeks, we can consider murine model of chronic tympanic perforations when applying mitomycin C prior to incisional myringotomy and associate dexamethasone. The duration of the tympanic perforations in our model, greater than 3 months, would justify to increase trials to study this method for the treatment of otitis media with effusion without using ear tubes.