Description

• Mastitis is an inflammation of the breast parenchyma and possibly associated tissues (areola, nipple, subcutaneous [SC] fat).
• Usually associated with bacterial infection (and milk stasis in the postpartum mother)
• Usually an acute condition but can become chronic cystic mastitis

Epidemiology

• Predominantly affects females
• Mostly in the puerperium; epidemic form rare in the age of reduced hospital stays for mothers and newborns
• Neonatal form
• Posttraumatic: ornamental nipple piercing increases risk of transmission of bacteria to deeper breast structures: Staphylococcus aureus is the predominant organism.

• 3–20% of breastfeeding mothers develop nonepidemic mastitis.
• Greatest incidence among breastfeeding mothers 2 to 6 weeks postpartum
• Neonatal form occurs at 1 to 5 weeks of age, with equal gender risk and unilateral presentation.
• Pediatric form
• Around or after puberty
• 82% of cases in girls

Etiology and Pathophysiology

• Microabscesses along milk ducts and surrounding tissues
• Inflammatory cell infiltration of breast parenchyma and surrounding tissues
• Nonpuerperal (infectious)
  • S. aureus, Bacteroides sp., Peptostreptococcus, Staphylococcus (coagulase neg.), Enterococcus faecalis
  • Histoplasma capsulatum
  • Salmonella enterica
  • Rare case of Actinomyces europaeus
• Puerperal (infectious)
  • Staphylococcus aureus, Streptococcus pyogenes (group A or B), Corynebacterium sp., Bacteroides sp., Staphylococcus (coagulase neg.), Escherichia coli, Salmonella sp.
  • Methicillin-resistant S. aureus (MRSA)
• Rare secondary site for tuberculosis in endemic areas (1% of mastitis cases in these areas): single breast nodule with mastalgia
• Corynebacterium sp. associated with greater risk for development of chronic cystic mastitis
• Granulomatous mastitis
  • Idiopathic
    • Predilection for Asian and Hispanic women
    • Association with α₁-antitrypsin deficiency, hyperprolactinemia with galactorrhea, oral contraceptive use, Corynebacterium sp. infection, and breast trauma
    • Most women have a history of lactation in previous 5 years.
  • Lupus; autoimmune
• Puerperal
  • Retrograde migration of surface bacteria up milk ducts
  • Bacterial migration from nipple fissures to breast lymphatics
  • Secondary monilial infection in the face of recurrent mastitis or diabetes
  • Seeding from mother to neonate in cyclical fashion
• Nonpuerperal
  • Ductal ectasia
  • Breast carcinoma
  • Inflammatory cysts
  • Chronic recurring SC or subareolar infections
  • Parasitic infections: Echinococcus; filariasis; Guinea worm in endemic areas
  • Herpes simplex
  • Cat-scratch disease
• Lupus

Risk Factors

• Breastfeeding
• Milk stasis
  • Inadequate emptying of breast
    • Scarring of breast due to prior mastitis
    • Scarring due to previous breast surgery (breast reduction, biopsy, or partial mastectomy)
  • Breast engorgement: interruption of breastfeeding
• Nipple trauma increases risk of transmission of bacteria to deeper breast structures: S. aureus predominant organism
• Neonatal colonization with epidemic Staphylococcus
• Neonatal
  • Bottle-fed babies
  • Manual expression of “witch’s milk”
  • Can predispose to lethal necrotizing fasciitis
• Maternal diabetes
• Maternal HIV
• Maternal vitamin A deficiency (in animal models)

General Prevention

Regular emptying of both breasts and nipple care to prevent fissures when breastfeeding; also good hygiene, including hand washing and washing breast pumps after each use (1)[A]

Commonly Associated Conditions

Breast abscess