Osler node

**Definition:** Small (usually 2-15 mm), raised, erythematous to violaceous, PAINFUL nodules on the pulp (pads) of the fingers and toes, thenar/hypothenar eminences, or soles. They are transient (hours to days) and resolve spontaneously.

**Pathophysiology:** - Classically attributed to immune complex deposition with a local vasculitis (type III hypersensitivity), which is why they are listed as an immunologic phenomenon in the modified Duke criteria. - Some evidence supports septic microemboli with local immune response, particularly in acute S. aureus endocarditis. Biopsies sometimes show microabscesses with neutrophilic infiltrates, and occasionally organisms. - Most associated with subacute bacterial endocarditis (viridans streptococci), but can occur in acute disease (S. aureus).

**Clinical significance:** - Part of the modified Duke criteria (minor criteria, immunologic phenomena): Osler nodes, Roth spots, glomerulonephritis, positive rheumatoid factor. - Other minor criteria: predisposing heart condition or IV drug use, fever >38°C, and vascular phenomena (Janeway lesions, septic arterial emboli, mycotic aneurysm, conjunctival hemorrhages, pulmonary infarcts, intracranial hemorrhage). - Major criteria: positive blood cultures with typical organisms, and evidence of endocardial involvement (e.g., vegetation on echo, new valvular regurgitation).

**High-yield distinction: Osler node vs Janeway lesion** - Osler node: painful, raised, nodular, on finger and toe pads. Immune complex mechanism (immunologic). - Janeway lesion: painless, flat (macular) erythematous or hemorrhagic lesions on palms and soles. Septic microemboli (vascular/embolic) with microabscesses. - Mnemonic: "Osler = Ouch" (painful), "Janeway = no pain."

**Other associated findings in endocarditis:** Splinter hemorrhages (subungual), Roth spots (retinal hemorrhages with pale centers), new murmur, fever, and anemia of chronic disease.

**Differential for Osler-like nodes (rare):** Systemic lupus erythematosus, disseminated gonococcal infection, marantic endocarditis, hemolytic anemia, typhoid fever, and other vasculitides.

**Management:** Treat the underlying endocarditis. Obtain at least 3 sets of blood cultures before antibiotics, followed by TTE/TEE. Give empiric IV antibiotics (vancomycin ± additional coverage) and then tailor to cultures. Skin lesions resolve with treatment of the infection.

**Eponym:** Named after Sir William Osler, Canadian physician and a founder of Johns Hopkins Hospital.