Labyrinthitis

Introduction:

This is defined as an inflammatory disorder involving the inner ear / labyrinth. Clinically this condition causes disturbances of balance and hearing of varying degrees in the involved ear. Causes:

1. Bacterial infections

2. Viral infections

3. Autoimmune causes

4. Vascular ischemic causes

Pathophysiology:

Anatomically labyrinth is composed of an outer osseous framework surrounding the delicate membranous labyrinth which contains the peripheral end organs of hearing and balance. Membranous labyrinth include:

1. Utricle

2. Saccule

3. Semicircular canals

4. Cochlea

The labyrinth lies within the petrous portion of temporal bone. It communicates with the middle ear via the oval and round windows.

Infecting organism may find their way into the inner ear via:

1. Pre-existing fractures

2. Oval window

3. Round window

4. Congenital dehiscence involving the bony labyrinth

Viral labyrinthitis:

Is characterized by sudden unilateral loss of hearing and equilibrium. Vertigo is usually incapacitating and associated with vomiting. These patients are bed ridden. Vertigo usually subsides within 4-6 weeks. Hearing loss is confined to high frequencies and is sensorineural in nature. An attack of upper respiratory tract infection precedes the development of labyrinthitis. This condition should not be compared with vestibular neuronitis which involves only the vestibular nerves and spares the cochlear component. Varicella Zoster oticus is an unique form of viral labyrinthitis caused by reactivation of dormant varicella zoster virus. This reactivated virus is known to attack spiral ganglion.

Common viral causes of labyrinthitis:

1. Mumps

2. Measles

3. Rubella (congenital labyrinthitis)

4. Cytomegalovirus

Bacterial labyrinthitis:

can be potentially caused by meningitis / otitis media. This could be caused by direct invasion of membranous labyrinth by the infecting organism (suppurative labyrinthitis) causing permanent destruction of vestibular and cochlear end organs. In patients with meningitis spread of infections can be bilateral since infections can travel via the CSF and involve the inner ear fluids through the internal acoustic meatus / cochlear aqueduct. Bacterial infections involving the middle ear cavity can enter the labyrinth via erosion of lateral canal which is commonly seen in patients with cholesteatoma. Treatment is usually directed against infecting organism and supportive therapy. Suppurative labyrinthitis is usually followed by labyrinthitis ossificans where the whole of the membranous labyrinth gets ossified. Labyrinthitis ossificans indicates a permanently dead labyrinth.

Common bacterial causes of labyrinthitis include:

1. S. pnuemoniae

2. Haemophilus influenza

3. Streptococcus

4. Staphylococcus

5. Neisseria

6. Bacteroids

7. Proteus

8. Moraxella catarrhalis

Serous labyrinthitis:

This is a potentially reversible disorder caused by diffusion of bacterial toxins into the inner ear via the inflamed round window membrane. Studies have shown that the permeability of the round window membrane is increased when there is inflammation. This may cause diffusion of bacterial toxins and immune mediators into the inner ear causing transient impairment of the inner ear functions.

Autoimmune labyrinthitis:

This is an uncommon cause of sensorineural hearing loss. This may be caused by localized / general autoimmune reactions. Examples of general autoimmune disorders causing labyrinthitis include Wegener's granulomatosis and polyarteritis nodosa.