Subcutaneous Nodules in Acute Rheumatic Fever: The Exception
Statement A is the EXCEPTION - it is erythema marginatum, not subcutaneous nodules, that appears as an evanescent rash appearing and disappearing before the examiner's eyes. 1
Distinguishing Between the Two Skin Manifestations
The American Heart Association clearly differentiates these two major criteria:
Erythema marginatum (the evanescent finding):
- Unique, evanescent pink rash with pale centers and rounded or serpiginous margins 1
- Present on trunk and proximal extremities, not facial 1
- Heat can induce its appearance and it blanches with pressure 1
Subcutaneous nodules (NOT evanescent):
- Firm, painless protuberances found on extensor surfaces 1
- Located at specific joints including knees, elbows, wrists, occiput, and along spinous processes of thoracic and lumbar vertebrae 1
- These are persistent lesions, not transient 2
Verification of the Other Statements
Statement B is TRUE:
- Subcutaneous nodules are firm, small (typically 0.5 cm), mobile lumps beneath the skin overlying bony prominences 1
Statement C is TRUE:
- While not explicitly stated as "2-3 weeks" in the guidelines, subcutaneous nodules are indeed a delayed manifestation 2
- They appear in 0-10% of ARF cases, making them one of the rarer major criteria 1
Statement D is TRUE:
- Nodules are more often observed in patients who also have carditis 1
- One study found 90.4% of patients with subcutaneous nodules had associated carditis 2
- However, carditis is not invariably present - approximately 9.5% of patients with nodules may not have carditis 2
Clinical Pearls
Duration and persistence:
- With treatment, most nodules disappear within 4 weeks (69% of cases), though some persist 5-8 weeks (19%) or even 9-12 weeks (7%) 2
- In rare cases (4.7%), nodules can persist beyond 12 weeks despite resolution of other disease activity 2
Number of nodules:
- Average number is approximately 18 nodules (range 4-49) 2
- Contrary to older teaching, not all patients present with large crops - 30.9% have fewer than 10 nodules 2
Diagnostic significance: