The occurrence of sudden unilateral or bilateral total deafness is considered a medical emergency. The worldwide incidence of sudden hearing loss has been estimated at around 15,000 cases per year; this number nevertheless reflects that a bilateral sudden hearing loss is rare, only about 2% of the cases.

The four most prevalent causes of sudden sensorineural hearing losses are trauma (head or pressure injury), vascular accident, viral infection and auto-immune disease. There are numerous less common causes, and the significant proportion with no clear cause is termed ‘idiopathic’. Otolaryngologists commonly initiate various treatments to optimize the chances of hearing recovery. However, despite any of these treatments, the literature reports recovery in on ly 30-70% of patients.

Sydney Cochlear Implant Centre (SCIC) has identified 20 idiopathic cases of rapidly progressing or sudden bilateral total hearing loss that did not respond to treatment, that were referred for cochlear implantation over the last 14 years. A detailed review revealed an interesting common factor – a history of long term, mostly self-prescribed and unmonitored consumption of medication containing codeine. Previous literature identified a few cases associating hearing loss with Hydrocodone – a synthetic opiod in which codeine and thebaine (a stimulant) are the base materials, and with Oxycodone (derived from thebain alone), both commonly available in the US. The majority of cases appear to be related to abuse of painkilling medication taken for recreational purposes. In Australia, analgesic preparations are only available without prescription over-the-counter when containing under 15mg of codeine, and always in combination with paracetamol, aspirin or ibuprofen. The figure varies significantly amount countries.

As part of the candidacy evaluation for cochlear implantation, the investigation at SCIC revealed long-term histories of chronic pain medicated with preparations containing codeine. All cases reported a genuine original cause for the chronic pain, which was initially medicated by the family doctors. However, over time, patients reported self-medicating and/or supplementing the analgesics received. Several of these cases still report a strong and continuing dependence on codeine. The group of patients reported only taking codeine in combination with paracetamol, even though it is available in other combinations, and the brand names varied.

Blood tests were also performed as part of the investigation for sudden hearing loss. All cases were indicative of macrocytosis (enlarged red blood cells). A retrospective review of previous and subsequent blood tests from these patients was requested from their referring doctors. A surprising and original finding was that the highest level of macrocytosis coincided with the onset of hearing loss as reported by the patients. The relationship between the enlarged red blood cells and the sudden and total hearing loss, or indeed the physiological mechanism involved, is unknown. Considering that the prescription of codeine-related medication has escalated from around 40 million in 1991 to nearly 180 million in 2007 (mainly in the US) and only a few cases of total deafness have been identified, finding predictive risk factors of sudden deafness will be a challenge. The Australian experience of addiction to painkilling medication is not too far behind.

A positive outcome is that the cochlear implant results for this group are generally superior to those for the average post-lingual implant recipient, when tested in a sound-proofed booth with recorded materials:

ACQUIRED HEARING LOSS                    SENTENCE SCORES                      SINGLE WORD SCORES

Codeine cases                                             94%                                                 50%

Average adult cases                                     82%                                                 32%

This summary was prepared by Neville Lockhart with the permission of Monica Bray of SCIC, from a detailed study by Freeman, Bray, Gibson and Amos, accepted for publication in the journal Acta Laryngological 2009.

Pills image:  Darren Robertson / FreeDigitalPhotos.net
Pill bottles & doctors bag: vitasamb2001 / FreeDigitalPhotos.net