What are the diagnostic criteria for rheumatoid arthritis?
- Morning stiffness lasting >1 hour
- Arthritis of 3 or more joints
- Hand joint arthritis
- Symmetrical joint involvement
- Rheumatoid factor positivity
- Periarticular erosions
- Rheumatoid nodules
A patient is classified as having rheumatoid arthritis if 4 of these 7 criteria are present. The first 4 must be present for >6 weeks.
Assays for anti-CCP antibodies can also be helpful in the diagnosis of RA, though they have not been included to date in the classification criteria. Anti-CCP antibodies are more specific (~90%) for rheumatoid arthritis than RF and they have a similar sensitivity. Their presence also predicts erosive disease.
What are the 5 major diagnostic features of polymyositis and dermatomyositis?
- Proximal muscle weakness
- Myopathic features on EMG testing
- Elevated muscle enzymes (Primarily the CK, though elevations of AST and LDH are also seen).
- Presence of a typical skin rash (in the case of dermatomyositis)
- Positive muscle biopsy (note that the histological features of PM and DM are different. PM is characterized by endomyseal infiltration of inflammatory cells, most of which are CD4+ cells. In DM, an inflammatory infiltrate is seen in the perivascular and perifascicular regions).
Name three drugs that cause hyperuricemia and may contribute to gouty arthritis. What antihypertensive drug lowers uric acid levels?
- Nicotinic acid
- Thiazide diuretics
You can remember these using the mnemonic “CAN’T LEAP”.
The ARB losartan has a uric acid-lowering effect.
Which 5 joints are most commonly affected in rheumatoid arthritis?
- MCP joints
- Wrist joints
- PIP joints
- MTP joints
Less frequently involved joints are the ankles, C-spine (particularly C1-C2), elbow, hip and TMJ.
Name 4 reasons for a spuriously elevated ESR.
- End-stage renal disease
- Advanced age
- Female sex
As a general rule, expected elevations in ESR due to advanced age or sex can be calculated according to the following equation:
ESR (mm/hr) >age (+ 10 for women) / 2