What are the causes of axillary lymphadenopathy?

Causes of Axillary Lymphadenopathy

Axillary lymphadenopathy is most commonly caused by benign conditions, including infections, inflammation, and reactive changes, though malignancies such as breast cancer, lymphoma, and metastatic disease from non-breast primary sites must be excluded. 1, 2

Common Causes of Axillary Lymphadenopathy

Benign Causes

• Infections:

  • Bacterial infections (local skin infections, cellulitis)
  • Viral infections
  • Tuberculosis (reactivation TB can present as isolated axillary lymphadenopathy) 3
  • Abscess formation

• Inflammatory/Autoimmune Conditions:

  • Rheumatoid arthritis
  • Collagen vascular diseases
  • Sarcoidosis
  • Granulomatous diseases

• Reactive Changes:

  • Non-specific reactive lymphadenopathy (most common benign cause) 4
  • Post-vaccination (particularly COVID-19 mRNA vaccines) 5

• Other Benign Causes:

  • Silicone adenitis in patients with breast implants 1
  • Accessory breast tissue abnormalities 1
  • Breast implant-related lymphadenopathy 1
  • Amyloidosis 6

Malignant Causes

• Breast Cancer:

  • Primary breast malignancy (most common malignant cause of axillary lymphadenopathy) 1
  • Occult breast cancer (can present as isolated axillary lymphadenopathy) 1

• Hematologic Malignancies:

  • Lymphoma (particularly non-Hodgkin lymphoma)
  • Leukemia (especially chronic lymphocytic leukemia) 4

• Metastatic Disease:

  • From non-breast primary sites
  • From unknown primary tumors 6, 4

Diagnostic Approach

Initial Evaluation

1. Age-appropriate imaging:

   • Patients <30 years: Ultrasound of axilla
   • Patients ≥30 years: Ultrasound plus diagnostic mammogram 1, 2

2. Ultrasound features suggesting malignancy:

   • Cortical thickness >0.3 cm
   • Absence of fatty hilum
   • Rounded shape
   • Size >2 cm (specificity 97% for malignancy when >33 mm) 2, 4
   • Ill-defined or spiculated margins 4

Further Workup

• Core needle biopsy for suspicious lymph nodes (preferred over FNA with sensitivity of 88% vs 74%) 2
• MRI breast if biopsy shows malignancy of breast origin but no abnormality on ultrasound/mammogram 1
• Additional testing based on clinical suspicion:
  • CBC with differential
  • CRP and ESR for suspected infection
  • ANA, Anti-Ro/SSA, Anti-La/SSB for suspected autoimmune disease 2

Clinical Significance

• In patients with isolated axillary masses, approximately 52-62% may have underlying malignancy 6
• When cancer is identified in axillary lymph nodes, breast cancer is the most common cause 1
• In a study of 31 patients with isolated axillary masses, 9 of 17 cancer cases had occult breast cancer 1
• Only 7% of biopsied abnormal nodes detected on axillary ultrasound are malignant in women with no personal history of breast cancer 2

Management Considerations

• Palpable axillary masses with negative/benign imaging should be clinically managed based on level of clinical suspicion 1
• For malignant axillary nodes with confirmed breast mass, refer to appropriate breast cancer guidelines 1
• For abscess formation, ultrasound-guided incision and drainage is recommended (80% success rate) 2
• For reactive lymphadenopathy post-vaccination, follow-up imaging may be appropriate based on risk stratification 5

Recognizing the diverse etiologies of axillary lymphadenopathy is crucial for appropriate management and to avoid unnecessary procedures while ensuring timely diagnosis of potentially serious conditions.