Otalgia pathophysiology

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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]; Associate Editor(s)-in-Chief: Raviteja Guddeti, M.B.B.S [2]

Overview

Otalgia or ear pain is one of the most common complaints in the pediatric age group presenting to the primary care or emergency room. Otalgia can be primary or referred. Primary being caused by diseases of the ear and referred being caused by diseases elsewhere. The ear canal is heavily innervated, and the skin lining the canal lies directly against the bone without an intervening subcutaneous layer; therefore, even mild pressure, swelling, or inflammation in this area can cause immediate and severe pain.

Pathophysiology

Primary Otalgia

• Otitis media: Eustachian tube (ET) dysfunction is the most important factor in middle ear disease. Interference with this mucosa, at the pharyngeal end of the eustachian tube facilitates direct extension of infectious processes from the nasopharynx to the middle ear, causing OM. Developmental alterations of the eustachian tube, an immature immune system, and frequent infections of the upper respiratory mucosa all play major roles in acute otitis media development in children.

• Otitis externa: Excessive exposure to water results in an overall reduction in cerumen production in the ear. This reduction in cerumen can then lead to drying of the external auditory canal and pruritus. The pruritus can then lead to probing of the external auditory canal, resulting in skin breakdown and an entry site for infection. The most common offending organisms are Pseudomonas aeruginosa, Staphylococcal aureus, anaerobes and gram-negative organisms, and fungi such as the Aspergillus and Candida species. It is common in swimmers and hence the name swimmer's ear.

• Mastoiditis: The pathophysiology of mastoiditis is straightforward: bacteria spreads from the middle ear to the mastoid air cells, where the inflammation causes damage to the bony structures. Streptococcus pneumoniae, Streptococcus pyogenes, Staphylococcus aureus, Haemophilus influenzae, and Moraxella catarrhalis are the most common organisms recovered in acute mastoiditis. Organisms that are rarely found are Pseudomonas aeruginosa and other gram-negative aerobic bacilli, and anaerobic bacteria.

• Cholesteatoma: Cholesteatoma may be congenital or acquired. Congenital cholesteatomas are usually epidermal cysts which have arisen as a result of a developmental abnormality. Acquired cholesteatomas predominantly arise following retraction of part of the ear drum in response to middle ear inflammation. Much less often they may arise as the result of migration of squamous epithelium through a perforation in the ear drum. Cholesteatoma may also arise as a result of metaplasia of the middle ear mucosa or implantation following trauma.

Referred Otalgia

The ear is supplied by a number of different sensory nerves, including cranial nerves V, VII, IX, and X, as well as the cervical plexus. Diseases affecting structures innervated by these nerves may result in referred (ie, secondary) otalgia.

• The auriculotemporal branch of the mandibular division of cranial nerve V (ie, V3) innervates the skin of the tragus and part of the helix of the external ear, the anterior and superior walls of the external auditory canal, and the anterior portion of the tympanic membrane. Ear pain can also be referred via cranial nerve V from the teeth, gums, mouth, jaw, and face. Rarely, trigeminal neuralgia can cause otalgia.

• The facial nerve (VII) innervates the posterior tympanic membrane and part of the posterior wall of the external auditory canal. Disorders of teeth, temporomandibular joint and parotid glands can cause referred pain in ear.

• The glossopharyngeal nerve (IX) innervates the posterior portion of the external auditory canal and meatus, the posterior portion of the tympanic membrane, the mastoid, and the eustachian tube. The tympanic branch of cranial nerve IX ascends into the middle ear and forms the tympanic plexus before proceeding as the lesser petrosal nerve to the otic ganglion. Ear pain can also be referred via cranial nerve IX from the posterior tongue, tonsils, and pharynx.

• The auricular branch (Arnold's nerve) of the vagus nerve (X) innervates part of the cavum conchae (the vestibule to the external auditory canal), the posterior wall of the external auditory canal, and the posterior portion of the tympanic membrane. Ear pain can also be referred via cranial nerve X from the heart, pharynx, larynx, trachea, diaphragm, thyroid gland, and esophagus, among other thoracic and abdominal structures.

• The upper cervical nerves (C2 and C3), particularly the posterior branch of the great auricular nerve, innervate the posterior surface of the external ear and some of the cavum conchae. Ear pain can also be referred via the cervical plexus from structures in the neck and cervical spine.

• Somatic afferent fibers from cranial nerves V, VII, IX, and X as well as the cervical plexus (C2 and C3) all synapse in the spinal trigeminal nucleus in the caudal medulla and the upper cervical spinal cord.

Hence any disease of the ear or in the areas innervated by the nerves which also supply the ear can cause ear pain. Psychogenic otalgia is when no cause to the pain in ears can be found, suggesting a functional origin. The patient in such cases should be kept under observation with periodic re-evaluation.