When should you suspect Minamata disease?

When talking about Minamata disease, many people will think of fulminant cases of the disease and their dramatic movement disorders. However, many current chronic Minamata disease sufferers have a completely different clinical profile.

People who have lived in the coastal areas of the Shiranui Sea and have eaten a lot of seafood, and are showing symptoms such as numbness in the hands and legs, have a tendency to trip over things and suffer from cramps have also the possibility of being Minamata disease victims.

The symptoms of Minamata disease, as written above in “For Patients”, are characterized by a cortical type of sensory disturbance in which the extent of the sensory disturbance is difficult to assess and in which the range of symptoms is changeable. In moderate or severe cases systemic sensory disturbance is present.

Ataxia seems to not only be of cerebellar origin but also can be caused by sensory disorder (sensory ataxia). The degree varies depending on the severity. In addition, the severity changes when a patient’s physical condition changes or the mental strain they may be under varies in intensity

In more serious cases speech disturbance, auditory disturbance as well as a reduction in the visual field can be recognized. In cases with speech disturbance, articulation can become slurred and often pronunciation of the Japanese sounds, “pa” and “ra” become difficult. Auditory disturbance is not only characterized by difficulty in hearing but also by difficulty in understanding the meaning of words.

Diagnosis

People who consider that only fulminant Minamata disease is “Minamata disease” may wonder why people with milder symptoms are diagnosed as Minamata disease patients.

We define Minamata disease as, “the various health disturbances that are produced by eating seafood polluted by organic mercury”. Methylmercury is extremely toxic to the central nervous system. If the concentration is high, even short term exposure can cause serious disorders and even if the concentration is low, health disorders can be caused by long-term exposure.

Normally, when diagnosing a disease, the accepted procedure is to differentiate between the different levels of the disease and diagnose the severity accordingly. For some reason, when it comes to diagnosing Minamata disease, it is not unusual to hear members of the medical staff scoff and say, “Is that all?” when they observe mild cases. Now that more people with mild symptoms have begun to appear recently, it is very important to make the correct assessment as to the level of severity from case to case, so that even mild cases are diagnosed correctly.

For the diagnosis of Minamata disease a documented history of methylmercury exposure and the presence of the characteristic neurological disorders are enough. A general medical certificate was drawn up in April 2006 based on the results of medical research and legal decisions.

In examining a patient for medical certification the following six categories are used.

• A person who has a history of exposure to methylmercury through the consumption of contaminated seafood and has predominant four-limb sensory disorder.
• A person who has a history of exposure to methylmercury through the consumption of contaminated seafood and has generalized superficial sensory disorder.
• A person who has a history of exposure to methylmercury through the consumption of contaminated seafood and who fails a two-point discrimination test of the tongue
• A person who has a history of exposure to methylmercury through the consumption of contaminated seafood and who has perioral sensory disorder.
• A person who has a history of exposure to methylmercury through the consumption of seafood and who has concentric narrowing of the visual field.
• A person who doesn’t have the symptoms listed in A - E above but who has our long history of exposure to methylmercury through the consumption of contaminated seafood and also exhibits mental retardation, mental disorder or movement disorder which were caused by methylmercury.

In November 2006 we issued the following information guidelines, “General Remarks on Minamata disease Diagnosis” (available only in Japanese), which describe the diagnosis of Minamata disease.

Therapy and rehabilitation

The points below deal with the general treatment and rehabilitation of Minamata disease patients. Doctors responsible for treatment should take into consideration the condition of each patient before deciding on the specific therapy and rehabilitation needed.

Vitamins B12 and ATP (adenosine tri phosphate) are used in the pharmacotherapy of numbness.
For dizziness, Betahistine mesilate is used.
For cramps, Baclofen or Dantrium is often effective.

An intravenous drip of ATP and Niacin, which are also used in the treatment of SMON disease, are often effective in treating the numbness in limbs and unsteady posture. You will have to be on the lookout for venous pain that may appear as a side-effect. We often give ATP and 20 mg Niacin by an intravenous drip infusion for 30 minutes. We gradually increase the doze to 60 mg during the following two weeks.

Herbal medicine is also used depending on symptoms. We tend to use Keishi-bukuryo-gan and Keishi-ka-ryo-jutsubu-to to treat numbness in the hands, and for numbness in the lower limbs Gosha-jinki-gan is often used. In cases where the pain becomes more intense at night, there is a possibility of blood stasis, and Keishi-bukuryo-gan can be effective. However, Keishi-bukuryo-gan can cause side-effects in the gastric system. Shakuyaku-kanzo-to, administered to the patient before going to bed, can often give complete relief from cramps.

Pay close attention to side-effects such as high blood pressure or aldosteronism. Take extra caution if a treatment is being administered three times a day.

Hochu-ekki-to is effective in cases where the patient is feeling low spirited. Rikkunshi-to is useful in cases where the patient has a poor appetite and Sanso-nin-to taken before sleeping is effective against insomnia.

For the relief of pain such as the numbness associated with Minamata disease, physiotherapy such as a hot pack, low frequency waves, microwave treatments and kinesitherapy are effective.

At our clinic injecting 0.5% xylocaine at acupuncture points helps to reduce pain associated with arthralgia and myalgia,.