What is the etiology and pathophysiology of mastitis?

Etiology and Pathophysiology of Mastitis

Etiology

Mastitis is primarily an inflammatory condition of breast tissue that may or may not involve bacterial infection, with the majority of cases representing inflammation rather than true infection. 1

Lactational Mastitis

• Bacterial pathogens: Staphylococcus aureus and Staphylococcus epidermidis are the predominant causative organisms in acute mastitis, with corynebacteria implicated in granulomatous forms 2
• Incidence: Affects approximately 10% of breastfeeding women in the United States, typically occurring within the first 3 months postpartum 1
• Risk factors include:
  • Overstimulation of milk production through excessive pumping 1
  • Tissue trauma from aggressive breast massage 1
  • Poor infant latch and improper lactation technique 1
  • Frequent overfeeding that disrupts normal milk flow 1

Non-Lactational Mastitis

• Periductal mastitis and duct ectasia are common benign causes, particularly in women in their fourth decade of life 3
• Can occur at any age, including in males 4
• Predominantly inflammatory rather than hormonal in nature 5

Microbiological Considerations

• Loss of bacterial diversity in the breast microbiome distinguishes mastitic milk from healthy milk samples 2
• Increasing antibiotic resistance in causative species complicates treatment 2

Pathophysiology

Inflammatory Cascade

• Most cases begin as inflammation without true infection, which is why conservative management for 1-2 days is often sufficient 1
• The condition represents a spectrum from simple inflammation to established infection to abscess formation 1, 6

Clinical Manifestation

• Cardinal signs of inflammation include erythema (or hyperpigmentation in darker skin), warmth, and pain 1, 6
• Focal breast tenderness typically precedes visible skin changes 5
• Systemic symptoms such as fever and malaise indicate progression beyond simple inflammation 1

Progression Pattern

• Without proper treatment, inflammation can progress to:
  • Established bacterial infection requiring antibiotics 1
  • Abscess formation, particularly in immunocompromised patients 1
  • Premature cessation of breastfeeding 7

Pathophysiological Distinction from Malignancy

• Inflammatory breast cancer can mimic mastitis clinically but represents aggressive malignant tumor growth rather than infectious/inflammatory etiology 6
• Cancer-related mastitis must be excluded when symptoms fail to respond to appropriate treatment for infectious mastitis 6

Tissue-Level Changes

• Inflammation involves breast parenchyma and may extend to dermal lymphovascular structures 5
• In lactational cases, milk stasis and ductal obstruction contribute to the inflammatory process 1