Neurotological studies upon intoxication by organic mercury compounds

Area of Science:

• Neurology
• Toxicology
• Otolaryngology

Background:

• In 1965, an outbreak of illness linked to organic mercury compounds affected residents near the Aganogawa River, Japan.
• This event necessitated investigation into the neurological and audiological effects of mercury intoxication.

Purpose of the Study:

• To investigate the neurotological disturbances in 144 individuals suffering from organic mercurial intoxication.
• To identify the specific neurological and auditory pathways affected by chronic mercury exposure.

Main Methods:

• Utilized SISI and other tests to assess auditory recruitment.
• Employed Békèsy's audiometry (TTS) to classify auditory adaptation patterns.
• Recorded spontaneous, positional, and optokinetic nystagmus using electro nystagmography (ENG).

Main Results:

• Auditory recruitment was largely absent, except in cases with pre-existing inner ear deafness.
• Békèsy's audiometry revealed abnormal adaptation patterns (Type II and III) in a significant number of patients.
• Electro nystagmography showed abnormalities in nystagmus (spontaneous, positional, and optokinetic) in a majority of the cases.

Conclusions:

• Chronic mercurial intoxication primarily results in lesions affecting the retrocochlea.
• The oculomotor system within the brain stem and cerebellum is also significantly impacted by mercury toxicity.
• Neurotological assessments are crucial for diagnosing and understanding the extent of damage from organic mercury poisoning.