**Question:** Which is a minor criteria for diagnosis of RF according to modified Jones criteria?

A. Presence of a positive rheumatoid factor (RF) test
B. Presence of anti-citrullinated peptide antibodies (ACPA)
C. Presence of erosions on radiographs
D. Presence of extra-articular manifestations (EAM)

**Core Concept:** The modified Jones criteria are a set of diagnostic criteria for rheumatoid arthritis (RA), which are used to aid in the clinical diagnosis and classification of patients with RA. Minor criteria are less specific but increase the likelihood of RA when present.

**Why the Correct Answer is Right:** A minor criterion is defined as a finding that is less specific but increases the likelihood of RA when present. In this case, a positive rheumatoid factor (RF) test is a minor criterion. RF is an autoantibody that targets the Fc region of IgG and IgA antibodies, and its presence is associated with an increased risk of RA development.

**Why Each Wrong Option is Incorrect:**

**Option A (Presence of a positive rheumatoid factor (RF) test):** Although a positive RF test is associated with RA, it is not specific enough to be considered a major criterion, as RF can be present in other conditions like infections and autoimmune diseases.

**Option B (Presence of anti-citrullinated peptide antibodies (ACPA)):** While ACPA is a more specific marker for RA, it is not considered a minor criterion as it is a major criterion itself, increasing the likelihood of RA diagnosis.

**Option C (Presence of erosions on radiographs):** Erosions on radiographs are more indicative of established RA, making it a major criterion rather than a minor criterion.

**Option D (Presence of extra-articular manifestations (EAM)):** EAM are non-joint symptoms or signs that may be present in RA patients, but unlike erosions on radiographs, they are not specific enough to be considered a minor criterion.

**Clinical Pearl:** The modified Jones criteria are a combination of both major and minor criteria to increase the specificity and sensitivity of RA diagnosis. While RF and ACPA tests are both important in RA diagnosis, they are either major criteria or specific markers, not minor criteria. Erosions on radiographs and extra-articular manifestations are more indicative of established RA and are considered major criteria or clinical features.

**Correct Answer:** **Option C (Presence of erosions on radiographs)** is a minor criterion in the modified Jones criteria. Erosions on radiographs are more indicative of established RA, suggesting joint inflammation and damage over time. The presence of erosions in early RA is less common and may not be present at the time of RA diagnosis.