Approach to a (+) Rheumatoid Factor (RF)!
As we've all heard, RF is poorly named because (+) RF does not always = RA.
So, what is RF?
As we've all heard, RF is poorly named because (+) RF does not always = RA.
So, what is RF?
RF = IgM antibodies against Fc portion of IgG.
Thankfully, the mechanism of RF production allows the development of a nice diagnostic framework!
Thankfully, the mechanism of RF production allows the development of a nice diagnostic framework!
Vastly oversimplified, this is the mechanism for RF production:
Abnormal immune response (from rheumatic *or* chronic inflammatory disorder)
👇
Chronic antigen stimulation (from chronic infection *or* malignancy)
👇
RF production
Abnormal immune response (from rheumatic *or* chronic inflammatory disorder)
👇
Chronic antigen stimulation (from chronic infection *or* malignancy)
👇
RF production
What functions may RF have in combatting infectious diseases?
🦠 Immune complex clearance
🦠 Amplification of humoral response
🦠 Presentation of antigens to T cells
Ref: ncbi.nlm.nih.gov
🦠 Immune complex clearance
🦠 Amplification of humoral response
🦠 Presentation of antigens to T cells
Ref: ncbi.nlm.nih.gov
Given the mechanism of RF production (ie abnormal immune response 👉 chronic antigen stimulation 👉 RF production), a diagnostic framework can be broken down into:
Rheumatic vs. Non-rheumatic disorders
Rheumatic vs. Non-rheumatic disorders
%s in supra-script notation represent the frequency of RF positivity in that disease.
The diseases listed were highlighted in the prior cited review & UpToDate's review.
UTD (Table 1): uptodate.com
Prior review: ncbi.nlm.nih.gov
The diseases listed were highlighted in the prior cited review & UpToDate's review.
UTD (Table 1): uptodate.com
Prior review: ncbi.nlm.nih.gov
Given several entry points for RF production, it seems like *many* chronic inflammatory diseases (not listed in this schema) can be very easily included in the DDx.
So, what diagnoses should we highlight?
So, what diagnoses should we highlight?
DON'T MISS diagnoses include:
1) Bacterial endocarditis: can mimic RA & has high morbidity/mortality. Have a low threshold for TTE & BCx.
2) HCV (which can also cause cryo.): can mimic RA & cause long-term consequences, including cirrhosis & HCC.
1) Bacterial endocarditis: can mimic RA & has high morbidity/mortality. Have a low threshold for TTE & BCx.
2) HCV (which can also cause cryo.): can mimic RA & cause long-term consequences, including cirrhosis & HCC.
See a case of "Infective Endocarditis Masquerading as Rheumatoid Arthritis" here:
ncbi.nlm.nih.gov
ncbi.nlm.nih.gov
Finally, should highlight RF is detectable in 5-25% of people 65+ years of age.
Let me know how to make this approach better!
@MithuRheum @KirtanPatolia @AdamJBrownMD @AnnKumfer @rabihmgeha @DxRxEdu
@MithuRheum @KirtanPatolia @AdamJBrownMD @AnnKumfer @rabihmgeha @DxRxEdu
@DruvBhagavan @tony_breu Oh & if compatible clinical picture, then I would order those serologies you mentioned! I usually never see RF sent by our rheum consultants, though. (Probs since it adds little specificity.)
@DruvBhagavan @tony_breu So a real-world timeline would prob be: unexplained (+) RF (likely sent as RA screen) 👉 send additional rheum serologies if compatible clinical picture
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