What is skull base osteomyelitis?
Skull base osteomyelitis is a serious, potentially life threatening disease of the bones of the skull base most notably from the temporal bone.
It has several names. It was known by the name “Malignant External Otitis.” This was a misnomer as it was not a malignant disease. It behaves in a very aggressive manner. Therefore the name was changed to Skull base osteomyelitis. This means that it is an infection of the bones of the skull, notably the temporal bone in which the ear is housed.
How does it occur?
The most important predisposing factor is that the person’s immune system is very weak and is unable to fight off and over come the infection.
The overwhelming majority of persons who suffer from skull base osteomyelitis also suffer from diabetes which is improperly controlled. Diabetes is now considered a major factor towards contributing to making a person’s immune system incompetent. Advanced age is another contributing factor.
HIV infections are becoming now a common cause of skull base osteomyelitis.
How do infections enter the temporal bone in which the ear is housed?
Most infections enter the ear and skull base through the external ear canal. This occurs by cleaning the ear canal with cotton buds, pins, toothpicks etc. This usually occurs at the junction between the cartilaginous and bony part of the external ear canal. An injury at this junction allows the infection to enter the tissues below causing rapid spread of the disease and then involves the bones of the skull base.
Skull base osteomyelitis can also occur following an infection of the middle ear. The infection then spirals out of control.
What germ (bacteria) is responsible for causing this infection?
The germ that is most often responsible for this infection is a germ called “Pseudomonas aeruginosa”.
This is a very tough bacteria and is difficult to eradicate and is resistant to many antibiotics.
What is the chief symptom of the effect of Skull base osteomyelitis?
The chief symptom is pain. The earache is unrelenting, often described as boring, and is always present. It does not go away with pain killers for long and soon returns immediately after the effect of the pain killer wears off.
Once the disease spreads the pain intensity increases and is then accompanied by facial nerve paralysis and paralysis of other nerves.
How does the physician make a diagnosis of skull base osteomyelitis?This is a clinical diagnosis.
- The patient is almost always a diabetic whose blood sugar is poorly controlled.
- The patient is usually in their sixties and above.
- There is a history of self-instrumenting the ear canal with an object like a cotton bud.
- A granuloma is often seen in the external ear canal.
- A CT scan of the temporal bones will demonstrate a moth eaten appearance.
- A gallium bone scan will demonstrate how active and fulminant the infection is.
What is the treatment of skull base osteomyelitis?
Surgery is contraindicated and should never be performed as it will hasten spread of the disease.
Surgery if at all is limited to biopsy of the granuloma of the external ear canal.
The mainstays of treatment are prolonged administration of antibiotics. This is usually given for a period of two to three months. Usually A ureidopennicillin is given. An Aminoglycoside can also be given.
The antibiotic needs to be given carefully in a hospital setup and the patient needs to be monitored carefully for side effects of the antibiotic. Kidney damage can occur.
Also the patient’s blood sugar needs to be monitored and controlled.
Topical antibiotics in the form of ear drops can be given. The external ear canal should be carefully cleaned to prevent reinfection.
Some physicians also give the patients hyperbaric oxygen.
How does the treating physician know that the infection is coming under control?
Once the pain starts to lessen and go away then that means that the infection is responding to the antibiotics.
The physician also gets a gallium bone scan later on will show if the infection has receded.
However the principal symptom is pain. If that resolves then the infection is resolving too.
The cranial nerves will also get back their normal function and is indicative of the infection resolving.
Can the skull base osteomyelitis infection return?Yes it can. This is usually the result of incomplete treatment. The treatment needs to be continued and the infection will then likely come under control.
Can it spread to the other ear?Yes it can.
- Skull base osteomyelitis is a serious life threatening condition.
- Pain is the cardinal symptom and most prominent feature.
- Nearly all patients suffer from diabetes that is improperly controlled.
- Quite a few patients are in their sixties and beyond.
- Surgery is contraindicated except for biopsying the granuloma in the external ear canal.
- Treatment consists of antibiotics given for a prolonged duration of three to four months.
- Survival is best if there is no cranial nerve involvement.
- Survival is poorest if there are other problems like kidney failure.