MM 261,279; ID 1462-1466
 
 

NAME OF DISEASE:     Otitis media

OVERVIEW:

Inflammatory disease of the mucosal lining of the middle ear with exudation is one of the most common infections besetting children. It is also one of the most frequently misdiagnosed and maltreated diseases. The acute form is almost invariably consequent to upper respiratory tract infection. Thus, although acute suppurative otitis media is a bacterial process, viral respiratory infection is important as an antecedent event. Aspiration of middle ear fluid in the syndrome of acute otitis media yields a bacteriologically sterile fluid in about 25% of cases.

In acute suppurative otitis media, Streptococcus pneumoniae causes more than half the cases at all ages. Haemophilus influenzae is mainly a pathogen of infancy, accounting for about one-third of the cases.

Before antibacterial antimicrobics were available, Streptococcus pyogenes was common, but it now is found in no more than 10-15% of cases. These three bacterial agents account for more than 90% of acute suppurative otitis media except in the newborn infant in whom coliform bacteria or staphylococci are often pathogens.

ETIOLOGICAL AGENTS:
 

MOST COMMON	RELATIVELY COMMON	UNUSUAL BUT IMPORTANT
Streptococcus pneumoniae	Staphylococcus aureus	Pseudomonas sp.
Haemophilus influenzae	Streptococcus pyogenes	Proteus sp.

PATHOGENESIS AND PATHOLOGY:

The eustachian tube is the principal portal for the entry of bacterial into the middle ear. Partial obstruction facilitates the ingress of nasopharyngeal bacteria into the middle ear or, in the case of complete obstruction, leads to negative pressure in the middle ear cavity and serous effusion.

Functions of the eustachian tube:

    1. Ventilation and pressure equilibration of the middle ear.
    2. Prevention of ingress of foreign material into middle ear.
    3. Egress of foreign matter and mucous from middle ear.

Anatomy, immunologic virginity, bottle propping and microbiologic inexperience conspire against the infant to produce a far greater frequency of otitis media in this age group than in older children and adults. The eustachian tube of the child, as compare to the adult:

    1. Is more horizontal
    2. Contains less cartilage
    3. Contains less stiff cartilage
    4. Has more patency
    5. Is more subject to intrinsic obstruction

These factors predispose the child to otitis media. Because he is exposed to a succession of infectious agents to which he has no immunity, mucosal swelling and adenoidal hypertrophy provide an ideal setting for pathogenic bacteria resident in the nasopharynx to establish themselves in the middle ear. Allergens may initiate the same process in allergic persons. Because almost all upper respiratory tract infections are caused by viruses, the usual sequence is viral infection, followed in 5-10 days by the onset of bacterial middle ear infection. Otitis media occasionally complicates streptococcal sore throat, but this is unusual.

The acute inflammatory response to the initiating viral infection or allergic reaction changes the thin, cuboidal lining of the middle ear cavity into a structure that is two to three times its normal thickness. The neutrophils of the acute inflammatory response migrate into the cavity to render purulent the initially serous fluid. As swelling involves the orifice of the eustachian tube, the lumen becomes occluded and exudate accumulates. As pressure increases, not only does the tympanic membrane bulge outward, but also pus may be forced into pneumatized portions of the petrous bone. Relief of the pressure is critical to resolution of the process and may occur through rupture of the eardrum.

CLINICAL SYMPTOMS:

The onset of suppurative otitis media is typically abrupt, producing pain in the ears, a feeling of fullness, and fever. The peripheral blood shows a moderate leukocytosis. There is no regional lymphadenopathy. There generally are no other symptoms except those of the viral respiratory infection or the allergic reaction that precedes the middle ear infection. However, in infancy, the major manifestations may be fever, ear pain, irritability, vomiting and loose stools. Unilateral otitis is twice as common as bilateral ear disease in infants.

In pneumococcal or streptococcal otitis media, inspection reveals a fiery red tympanic membrane with bulging and loss of all normal landmarks. Spontaneous perforation may occur in the first 24-48 hours, resulting in alleviation of pain. The findings are generally less dramatic when H. influenzae is the etiologic agent. There is less redness and less tension on the tympanic membrane, and spontaneous perforation is uncommon. When there is a question about the presence of fluid in the middle ear, pneumatic otoscopy can be useful to demonstrate the degree of movement of the tympanic membrane in response to external pressure.

DIAGNOSIS:

In the presence of ear pain, fever, vomiting and diarrhea, middle ear effusion is definitive of acute otitis media. Check for normalcy of the tympanic membrane:

    1. Neutral position
    2. Flexible
    3. Transparent
    4. Ground glass appearance

These will change in otitis media. If the tympanic membrane is intact and myringotomy is decided on, the canal and surface of the tympanic membrane should be cleaned with 70% ethanol or iodine before the incision is made. Smears and cultures should be made from the pus on the myringotomy knife blade. Needle aspiration is preferred over myringotomy in most circumstances. It is less traumatic and a better specimen for culture is obtained. Pus should be inoculated in culture media appropriate to the isolation of the pathogens common to otitis media. However, middle ear effusion is not normally cultured.

TREATMENT:

    1. Relieve pressure by myringotomy (rupture of the tympanic membrane) or needle aspiration.
    2. Follow the management scheme on page 5

PREVENTION:

Purified polysaccharide vaccines for prevention of infection by:
    Streptococcus pneumoniae (PNU-IMMUNE or Pneumovax) - each dose of the
    multivalent vaccine provides 23 types of capsular polysaccharide covering the majority of strains causing ottis media.
    Recommended for children over 2 years of age.

    Streptococcus pneumoniae (Prevnar) - each dose of the multivalent vaccine provides 7 types of capsular polysaccharide
    conjugated to a non-toxic diphtheria toxin. Recommended for children at 2, 4, 6 and 12 months of age.

    Haemophilus influenzae - each dose of the monovalent vaccine provides the capsule polysaccharide from serotype b organisms
    conjugated to a protein. Recommended for children at 2, 4, 6 and 15 months of age.
 

NAME OF DISEASE:     Otitis externa, Swimmer's Ear

OVERVIEW:

Otitis externa is an infection of the external ear canal which can assume a benign or malignant form. The benign form occurs in those who have chronic moisture in the external ear canal. The malignant form occurs in elderly diabetics.

ETIOLOGICAL AGENT:    Pseudomonas aeruginosa

DIAGNOSIS:

There are two forms of this disease, benign and malignant. The benign form is a superficial infection of the external auditory canal that is frequently initiated by moisture. The patient complains of pain, itching and a sensation of fullness in the ear. Exudate, erythema and edema may be seen in the canal. Although the tympanic membrane may be involved, it moves well with the pneumatic otoscope in contrast to the immobility seen in otitis media.

Malignant otitis externa is seen in elderly diabetics and has a 20% fatality rate. The infection rapidly spreads to the adjacent soft tissues and bone structures. The seventh cranial nerve becomes infected at its exit from the stylomastoid foramen resulting in Bell's palsy. Later cranial nerves X, XI and XII become involved.

TREATMENT:

Benign otitis externa - eardrops containing polymyxin B, neomycin, hydrocortisone and selerum sulfide

Malignant otitis externa - Imipenem cilistatin or meropenem or ciprofloxacin or ceftax