Can mycotic aneurysms occur in the context of syphilis?

Mycotic Aneurysms and Syphilis

Yes, the term "mycotic aneurysm" can technically apply to syphilitic aneurysms, but this is a misnomer that causes confusion—syphilitic aortitis causes true aneurysms through a distinct chronic inflammatory mechanism, not the acute infectious process that defines modern mycotic aneurysms. 1

Understanding the Terminology Confusion

The term "mycotic aneurysm" was originally coined by Osler to describe infected aneurysms, but this historical nomenclature is misleading in the context of syphilis 1:

• Osler's original term "mycotic endarteritis" encompassed all infected aneurysms, including those from syphilis 1
• Modern usage has evolved: The term "mycotic aneurysm" now predominantly refers to acute bacterial or fungal infections of arterial walls, while "infected aneurysm" or "infectious aortitis" are preferred terms 1
• Syphilitic aneurysms are pathophysiologically distinct from what we now call mycotic aneurysms 1

Key Differences Between Syphilitic and Mycotic Aneurysms

Syphilitic Aortitis Characteristics:

• Delayed presentation: Thoracic aortic aneurysm appears 10 to 25 years after initial spirochetal infection 1
• Location: Predominantly affects the ascending thoracic aorta 1
• Mechanism: Chronic inflammatory destruction of the vasa vasorum leading to medial layer weakening 1
• Morphology: Typically fusiform aneurysms, though can be saccular 2, 3
• Associated findings: Often accompanied by aortic valve insufficiency (nearly 50% of cases) and coronary ostial stenosis 1, 4

True Mycotic Aneurysms:

• Acute presentation: Develops rapidly during active bacteremia or sepsis 1
• Common organisms: Staphylococcus aureus and Salmonella are most frequent 1
• Morphology: Predominantly saccular aneurysms or pseudoaneurysms 1
• Mechanisms: Septic emboli, hematogenous seeding, or contiguous spread from adjacent infection 1
• Blood cultures: Positive in 50-90% of cases 1

Clinical Recognition of Syphilitic Aortitis

When evaluating for syphilitic involvement:

• Suspect in patients with ascending aortic aneurysm and risk factors for untreated syphilis 3, 5
• Look for associated cardiovascular manifestations: aortic regurgitation, coronary ostial disease 1, 4
• Consider neurosyphilis evaluation: Argyll Robertson pupil, CSF abnormalities 6
• Serologic confirmation: Both nontreponemal (RPR/VDRL) and treponemal tests required 1, 2
• Imaging characteristics: Unlike acute mycotic aneurysms, syphilitic aneurysms may show calcification and develop over years 3, 6

Important Clinical Pitfalls

Do not confuse the chronic, indolent course of syphilitic aortitis with acute mycotic aneurysms, which require urgent surgical intervention due to high rupture risk 1. Syphilitic aneurysms:

• Develop over decades, not days to weeks 1
• Require antibiotic therapy (IV penicillin) plus surgical repair when aneurysm is present 3, 4
• Have different imaging characteristics (less periaortic inflammation, no gas, chronic appearance) 1
• Blood cultures are typically negative unless concurrent bacteremia from another source 2, 3

Management Approach

For confirmed syphilitic aortitis with aneurysm 3, 4:

• Antibiotic therapy: IV penicillin G per CDC guidelines for tertiary syphilis 1
• Surgical intervention: Required for ascending aortic aneurysm with aortic valve replacement if indicated 2, 3, 4
• Timing: Unlike acute mycotic aneurysms requiring emergency surgery, syphilitic aneurysms allow for planned surgical repair after antibiotic initiation 3, 5

The bottom line: While historically grouped under "mycotic aneurysms," syphilitic aortitis represents a distinct chronic inflammatory vasculopathy requiring different diagnostic and therapeutic approaches than acute bacterial mycotic aneurysms.