What are the causes of mitral stenosis?

Causes of Mitral Stenosis

Rheumatic heart disease is the predominant cause of mitral stenosis, accounting for approximately 85% of all cases worldwide. 1

Primary Etiologies

Rheumatic Heart Disease

• Most common cause globally (85% of cases) 1
• Results from rheumatic fever following group A β-hemolytic streptococcal infection 2
• Pathological features include:
  • Commissural fusion
  • Leaflet thickening, particularly at the tips
  • Chordal fusion
  • Restriction of leaflet mobility 1
  • Creates a characteristic "funnel-shaped" mitral apparatus 1

Degenerative Mitral Stenosis

• Becoming increasingly prevalent in developed countries with aging populations 1, 3
• Accounts for approximately 12% of mitral stenosis cases referred to hospitals 1
• Characterized by:
  • Mitral annular calcification (MAC)
  • Valve thickening
  • Chordal shortening
  • Typically affects posterior leaflet first, with relative preservation of anterior leaflet mobility 1
  • No commissural fusion (important distinction from rheumatic MS) 1

Congenital Mitral Stenosis

• Rare cause, mainly observed in infants and children 1
• Various subtypes include:
  • Mitral annular hypoplasia
  • Subvalvular mitral stenosis
  • Supravalvular or intravalvular mitral ring 4
  • Frequently associated with abnormal papillary muscle arrangements and other congenital cardiac defects (84-97% of cases) 1

Uncommon Causes

Infective Endocarditis

• Active infection can cause valve obstruction through vegetations 5
• More commonly causes regurgitation than stenosis

Left Atrial Myxoma

• Can cause functional mitral stenosis by obstructing the mitral valve orifice 1

Ball Valve Thrombus

• Large thrombus in left atrium can obstruct mitral inflow 1

Severe Annular Calcification

• Can progress to cause stenosis, particularly in elderly patients 1, 3
• More common in patients >50 years of age 1

Mucopolysaccharidosis

• Rare metabolic disorder that can affect valve structure 1

Iatrogenic

• Rare complication following certain cardiac procedures

Age and Geographic Distribution Patterns

• Rheumatic MS tends to present in younger patients, including during pregnancy 1
• Degenerative MS is associated with increased age, more common in developed countries 1, 3
• Rheumatic heart disease remains highly prevalent in developing countries 2, 6
• Incidence of rheumatic fever had declined in Western countries but is seeing a resurgence due to immigration from non-industrialized countries 2

Clinical Implications

• The etiology of mitral stenosis significantly impacts treatment options:

  • Rheumatic MS with commissural fusion is amenable to percutaneous mitral commissurotomy 1
  • Degenerative MS is not amenable to percutaneous procedures due to absence of commissural fusion 1
  • Valve replacement is typically the only option for severe non-rheumatic MS 1

• Understanding the underlying cause is essential for proper management and prognostication, as rheumatic and degenerative MS display significant differences in pathophysiology, prognosis, and disease progression 3