**Question:** Which of the following is a major criteria for diagnosis of Rheumatic fever (RF) according to modified Jones criteria

A. Cardiac involvement
B. Sydenham's chorea
C. Joint involvement
D. Central nervous system manifestations

**Core Concept:**
Rheumatic fever (RF) is an illness that occurs as a consequence of an untreated streptococcal infection, primarily affecting children and young adults. The modified Jones criteria are a set of diagnostic standards used to identify RF. Major criteria are essential for diagnosis and include symptoms that indicate severe and systemic involvement of different organ systems.

**Why the Correct Answer is Right:**
The correct answer, **C. Joint involvement**, is a major criteria for diagnosis of RF according to the modified Jones criteria. Joint involvement often presents as polyarthritis, which is characterized by the involvement of multiple joints simultaneously. This type of arthritis is typically symmetrical and affects the large joints, such as the knees, ankles, elbows, and wrists.

**Why Each Wrong Option is Incorrect:**

**A. Cardiac involvement**: While cardiac involvement is a component of RF, it is not considered a major criteria. Cardiac involvement often presents as valvular lesions, heart failure, or pericarditis, which may be present in RF but are not sufficient for diagnosis on their own.

**B. Sydenham's chorea**: Sydenham's chorea is a type of involuntary movement disorder caused by RF. However, it is not a major criteria for diagnosis according to the modified Jones criteria. Sydenham's chorea is a clinical sign and not a direct indicator of RF diagnosis.

**D. Central nervous system manifestations**: Central nervous system involvement is a component of RF, but it is not a major criteria. Central nervous system manifestations could include carditis, chorea, or encephalitis, which are not sufficient for diagnosis.

**Clinical Pearl**: In clinical practice, the modified Jones criteria are used to diagnose RF. While all components of RF are essential for the diagnosis, the criteria emphasize the importance of joint involvement as a major criteria, as it is a fundamental indicator of the disease process.