Deshpande J

Department of Pathology, T. N. Medical College and B. Y. L. Nair Charitable Hospital, Mumbai - 400 008, India.

Non-specific aortoarteritis (NSAA) also known as Takayasu's arteritis was first described in Japan in the mid 20 ^th  century and has subsequently become a specific established entity, particularly with improved diagnostic facilities, interventional modalities and cardiovascular surgical techniques. Though the disease is prevalent worldwide it is more common in developing Afro- Asian countries and in Japan. The autopsy incidence of this disease at K. E. M. hospital, Mumbai is 15%, with 20-30 new cases being identified every year at this hospital alone. Japan made planned attempts to study this disease and estimated that 50-80 new patients are diagnosed every year, with an autopsy incidence of 33%.

The disease possibly starts at a young age when patients may present with non-specific constitutional symptoms. The mortality is high in children because of rapid development of hypertension and congestive cardiac failure (CCF). CCF is often a major problem in children. Myocarditis may occasionally be seen in children causing failure. Cardiomyopathy is often suggested as a cause for CCF. However, the histological features of cardiomyopathy are non-specific and the presence of rapidly developing pressure overload in NSAA itself may be the cause of CCF. In children, the autopsy specimens of aorta commonly shows a localized disease, particularly in the abdominal aorta, with the absence of secondary changes like atheroma and calcification. The uninvolved segments of aorta have raised gelatinous plaques, which are composed of abundant ground substance (acid mucopolysaccharides). In the radiological interpretation of lesions, the clinical findings are important, the most important criteria being onset of disease before the age of 40 years. Atherosclerosis frequently obscures the characteristic lesions of NSAA.

An extensive involvement of the aorta is more common than isolated involvement of the small segments. A geographic variation has been noted in the distribution of lesions. Disease of abdominal aorta and renal arteries is more common in our country while in Japan involvement of the thoracic aorta (ascending and descending) is more common, with frequent involvement of arch vessels and low incidence of disease involving the renal arteries. Both radiologically and in autopsy specimens, different types of lesions are noted- stenotic, dilatation, occlusive (due to mural thrombus), aneurysmal, and irregular lesions. There is preferential involvement of left subclavian and renal arteries with sparing of infrarenal segments of aorta. Aortic branches are generally involved when there is significant aortic disease. In less than 15% cases, angiographically only branch vessel disease can be identified. Marked periaortic adhesions, lymph node enlargement and dilatation of lymphatics is striking in some cases.

The natural course of the disease is difficult to establish. In some ways the disease pattern resembles rheumatic heart disease. A small number of patients give a history of constitutional symptoms with absent pulses, which is likely to be the acute phase of the disease. This feature may be lacking in the majority cases because of the mild transient nature of the acute attacks. The chronic phase characterized by circulatory deficits is seen after a variable period. Even paediatric cases show healed lesions indicating that inflammation is self-limiting in majority of cases. A small subset may have repeated acute attacks and histologically the aorta will show acute and healed lesions. Regression of lesions is however extremely uncommon. After diagnosis survival depends on many factors. Prognosis depends on complications, clinical course, and age of patients. The 15-year survival rate of patients with and without complications was 66.3% vs. 96.4%. Survival is better in patients without progressive course and those below 35 years of age. Early diagnosis with proper medical or surgical management is essential for good prognosis Since 1980, percutaneous transluminal angioplasty has been used for treating these vascular lesions, the most common indication being uncontrolled hypertension with angiographic evidence of stenosis and pressure gradients. The incidence of major complications is around 3-13 %. Failure is often due to unfavourable angiographic morphology. Restenosis is frequently observed and it mostly occurs in patients with residual stenosis and pressure gradients.

The injurious agents, whatever it may be reach the outer coat of the aorta first, by lymphatics, vasa vasora or by direct extension. The maximum inflammatory reaction is at the junction of adventitia and media and subsequently extends to involve the media. Grossly this is seen as peraortic adhesions with reactive lymph node enlargement. The lack of intimal inflammation excludes possibility of deposits of immune complexes on the aortic intima. The association of tuberculosis and aortitis has been much debated. Cases of tuberculous aortitis and NSAA are different in many respects, particularly the extent of disease and the proximity of the tuberculous focus to the aorta.

There are many aspects of this disease, which are ill understood. The exact aetiopathogenesis remains a problem, the geographic variation in the incidence, variations in the distribution of lesions and progression of this disease still remain an enigma.

Dr. Jaya Deshpande,
Department of Pathology,
T. N. Medical College and B. Y. L. Nair Charitable Hospital,
Mumbai Central, Mumbai, India