This disease is not related to circulatory system

The correct option is Diphtheria.

To understand why this is the correct choice, let us examine each of the options in relation to the circulatory system:
1. Diabetes mellitus: This is a metabolic disorder characterized by high blood sugar levels. Over time, chronic high blood glucose levels damage blood vessels and nerves, leading to serious cardiovascular complications such as coronary artery disease, heart attacks, and strokes. Thus, it is closely linked to circulatory system health.
2. Hypertension: Commonly known as high blood pressure, hypertension is a chronic medical condition where the force of the blood against the artery walls is consistently too high. It directly impacts the heart and blood vessels, making it a primary circulatory system disease.
3. Diphtheria: This is an acute, highly contagious bacterial infection caused by Corynebacterium diphtheriae. It primarily affects the mucous membranes of the respiratory tract (specifically the nose and throat), causing a characteristic thick, gray membrane to form. Because it is fundamentally an infectious disease of the respiratory system rather than a disorder of the heart or blood vessels, it is classified as not related to the circulatory system.
4. Coronary thrombosis: This condition refers to the formation of a blood clot (thrombus) inside a coronary artery, which supplies blood to the heart muscle. Since it directly blockages blood flow within the circulatory network, it is a cardiovascular disease.

Therefore, Diphtheria is the only disease among the options that is not directly related to the circulatory system.