Is Fibromuscular Dysplasia (FMD) the same as Spontaneous Coronary Artery Dissection (SCAD)?

Fibromuscular Dysplasia (FMD) and Spontaneous Coronary Artery Dissection (SCAD): Distinct but Related Conditions

No, Fibromuscular Dysplasia (FMD) and Spontaneous Coronary Artery Dissection (SCAD) are not the same condition, though they are strongly associated with each other. 1

Definitions and Pathophysiology

• FMD is a non-inflammatory, non-atherosclerotic arteriopathy affecting medium and small-sized arteries, characterized by a "string-of-beads" appearance on angiography 2, 1
• SCAD is defined by the spontaneous formation of an intramural hematoma within the coronary artery wall, with or without an intimal tear, leading to compression of the true lumen and potential myocardial infarction 2, 1
• SCAD is characterized by specific angiographic patterns including multiple radiolucent lumens, diffuse stenosis, or focal tubular stenosis that can mimic atherosclerosis 2

Relationship Between FMD and SCAD

• FMD is present in up to 72% of SCAD patients, representing the strongest association with SCAD 1, 3
• Studies show that FMD prevalence in SCAD patients ranges between 25%-86%, with variation explained by different screening techniques 3
• FMD may predispose patients to SCAD, but they remain distinct clinical entities 4, 3
• The frequent association raises the question of whether they are different facets of the same disease or distinct though related entities 4

Demographic Patterns

• Both conditions disproportionately affect women over men in approximately a 9:1 ratio 5
• SCAD predominantly affects young to middle-aged women without traditional cardiovascular risk factors 1
• Over 90% of SCAD cases occur in women, with a significant proportion occurring during the peripartum period 1

Diagnostic Considerations

• SCAD is diagnosed by coronary angiography, often supplemented by intracoronary imaging (OCT or IVUS) 2, 1
• FMD diagnosis requires imaging of extracoronary arterial beds, typically using CT or MR angiography 6
• In a study of 173 SCAD patients, the prevalence of FMD was 31.8%, with 29.1% of those patients having involvement of multiple vascular beds 6
• Coronary FMD (CFMD) is believed to be rare but may predispose patients to SCAD 7

Clinical Implications

• When SCAD is diagnosed, screening for FMD in other vascular beds is recommended 2, 1
• The management approach differs between the conditions:
  • SCAD typically requires conservative management in stable patients, as revascularization attempts can worsen dissections 1
  • FMD management focuses on blood pressure control and surveillance for aneurysms or dissections 1
• Beta-blockers are strongly recommended for long-term management of SCAD as they reduce recurrence risk 1

Important Distinctions

• Not all SCAD patients have FMD, and not all FMD patients develop SCAD 4, 6
• In a 5-year follow-up study, SCAD patients had recurrent myocardial infarctions, but primary extracoronary vascular events were rare 6
• Coronary tortuosity has been identified as a risk factor for SCAD recurrence, which may be related to its association with FMD 2

Understanding the distinction between these conditions is crucial for appropriate management and follow-up of patients with either or both conditions.