Myoamyoa disease is one of the rare diseases affecting the blood vessels of the brain. In this disease there is constriction of the arteries of the brain especially those located in the circular fashion at the base of the brain (circle of Wills) and also the arteries which form the circle of Willis. Adjacent to the obstructed arteries several tiny blood vessels arise in order to maintain adequate blood supply to the brain. These arteries are known as collaterals.
The term myoamyoa means “puff of smoke” in Japanese and it refers to the appearance of the collateral blood vessels adjacent to the obstructed blood vessels. Usually narrowing of the arteries occurs on both sides although one sided narrowing is also possible.

Causes
The exact underlying cause of myoamyoa disease is not known however this disease is considered to be hereditary. It is estimated that out of 100 patients of myoamyoa disease about 10 patients have positive family history for the disease. In humans two sets of chromosomes are present; one set is autosomes (22 pairs) and the other set is sex chromosomes (1 pair). Myoamyoa disease is considered to autosomal dominant as the suspected genetic abnormalities are located on the autosomes.
It is found that patients of Myoamyoa disease have high level circulating thyroid antibodies making them susceptible to thyroid related immunological diseases like thyrotoxicosis, Graves’ disease. Sometimes other medical conditions may also occur in patients of myoamyoa disease.
These diseases include
1. Infectious diseases like tuberculosis, leptospirosis
2. Blood disorders like Fanconi anemia, aplastic anemia, sickle cell anemia, lupus anticoagulant etc,
3. Congenital diseases like Down syndrome, Marfan syndrome, turner syndrome, Hirschprung disease etc
4. Blood vessel related disease like atherosclerosis, coarctation of aorta, injury to the blood vessels following exposure to radiation, injury to the cranium, high blood pressure etc
This disease is most common among Japanese people; however the disease may occur in people of other ethnic background like (whites, blacks, Hispanics etc).
The disease slightly more common in females and the incidence of the disease is the highest among children and then people in third and fourth decades are particularly at risk.

Treatment
Drug therapy does not give satisfactory results rather drugs are helpful in management of complications. Commonly used drugs are antihypertensive in a patient with bleeding (intracerebral haemorrhage) already suffering from high blood pressure, antiplatelet or anticoagulant drugs in patients who suffer from stroke especially in people suffering from ischemic stroke.
Surgical interventions recommended for treatment of the disease include anastomsis (connection) of several other arteries so that the blood supply to the brain remains more or less normal. These anastomisis include anastomisis between superficial temporal artery and middle cerebral artery, other surgical interventions include synangiosis characterized by fixing of healthy artery in place of the defective artery.

Prognosis
Death occurs in patients of myoamyoa mainly because of bleeding from collateral vessels. The principal factor determining the outcome of the disease depends upon extent of blood loss due to bleeding, frequency of episodes of bleeding etc.
In about 10% of the adults suffering from myoamyoa death can occurs whereas, in children about 5 children out of 100 children suffering from myoamyoa may die.
The disease is progressive in nature hence about 50 to 60 patients out of every 100 patients suffer from deterioration of cognitive functions of the brain; usually people suffering from repeated episodes of bleeding are at increased risk.