How should mastitis be diagnosed?

How to Diagnose Mastitis

Mastitis diagnosis is primarily clinical, based on focal breast tenderness accompanied by fever and malaise, with imaging (ultrasound first-line) used to exclude complications like abscess formation and differentiate from malignancy when presentation is atypical or fails to respond to treatment. 1

Clinical Diagnosis

The diagnosis of mastitis is typically straightforward and clinical:

• Lactational mastitis: History of breastfeeding with acute onset of focal breast pain, erythema, warmth, and systemic symptoms (fever, malaise) 1
• Duration and presentation: Symptoms develop rapidly, typically within days
• Physical examination findings: Localized tenderness, erythema, induration, and warmth in one breast

Critical distinction: Differentiate between infectious and noninfectious lactational mastitis, as infectious forms require intervention while noninfectious forms need only supportive care 2.

When Imaging is Indicated

Ultrasound (First-Line Imaging)

Ultrasound is the primary imaging modality for mastitis evaluation 3, 4. Perform ultrasound when:

• Suspected abscess formation (palpable mass, fluctuance, or failure to respond to antibiotics within 48-72 hours)
• Distinguishing simple mastitis from complicated forms
• Guiding drainage procedures
• Monitoring treatment response

Ultrasound findings that favor benign mastitis over malignancy 4:

• Ill-defined fluid collections or discrete abscess cavities
• Interstitial edema
• Edematous fat lobules
• Skin thickening (though extensive skin thickening may suggest malignancy)

Mammography (Selective Use)

Mammography has limited role in acute mastitis 3 but should be performed when:

• Age ≥30 years with atypical presentation
• Suspected non-lactational mastitis (always view with suspicion) 5
• Failure to respond to appropriate antibiotic therapy after 7-10 days 6
• Clinical concern for underlying malignancy

Red Flags Requiring Tissue Diagnosis

Obtain core needle biopsy (with or without skin punch biopsy) when 6:

• Mastitis symptoms persist despite 1 week of appropriate antibiotics 7
• Extensive skin thickening involving ≥1/3 of breast
• Peau d'orange (dermal edema)
• Infiltrated or matted axillary lymph nodes
• Any non-lactational mastitis presentation

Inflammatory Breast Cancer Exclusion

Inflammatory breast cancer (IBC) must be excluded when patients present with 7:

• Rapid onset (<6 months) of breast erythema and edema
• Erythema occupying ≥1/3 of breast
• Peau d'orange or warm breast
• History of "mastitis" not responding to ≥1 week of antibiotics

Diagnostic requirements for suspected IBC 7:

1. Core needle biopsy to confirm invasive carcinoma
2. Skin punch biopsy (at least two) to document dermal lymphovascular invasion
3. Diagnostic mammogram with ultrasound of breast and regional lymph nodes
4. Consider breast MRI if mammography/ultrasound non-diagnostic 6

Pathologic Confirmation

For chronic or granulomatous mastitis, pathologic confirmation is required 2:

• Core needle biopsy showing characteristic granulomatous inflammation
• Distinguish cystic neutrophilic granulomatous mastitis (CNGM) associated with Corynebacterium (treat with doxycycline)
• Culture specimens when infectious etiology suspected

Common Pitfalls

• Assuming all breast inflammation is simple mastitis: Non-lactational mastitis should always raise suspicion for malignancy 5
• Delaying imaging in treatment failures: Ultrasound should be performed promptly when antibiotics fail to improve symptoms within 48-72 hours
• Relying solely on negative imaging: A benign skin punch biopsy does not rule out inflammatory breast cancer when clinical suspicion remains high 6
• Over-reliance on mammography in acute phase: Ultrasound is superior for evaluating acute inflammatory changes 3, 4