Differential Diagnosis of Enlarged Inguinal Lymph Nodes
The differential diagnosis for enlarged inguinal lymph nodes includes malignancy (metastatic disease from genitourinary or lower extremity cancers, lymphoma), infectious causes (bacterial lymphadenitis, sexually transmitted infections), and reactive/inflammatory lymphadenopathy, with 30-50% of palpable inguinal nodes being inflammatory rather than malignant. 1
Malignant Causes
Metastatic Disease
- Genitourinary malignancies are the primary concern for inguinal lymphadenopathy, particularly penile cancer and vulvar cancer, which drain to the inguinal basin 2
- Melanoma from lower extremity or genital skin can metastasize to inguinal nodes 3
- Anal and urethral cancers may present with inguinal lymphadenopathy 2
- Among patients with penile cancer and palpable inguinal nodes, approximately 50% have metastatic disease while the other half have inflammatory changes 2
Lymphoma
- Both Hodgkin and non-Hodgkin lymphoma can present with inguinal lymphadenopathy 4, 5
- Lymphoma should be suspected when nodes are hard, matted/fused, or larger than 2 cm 5
Infectious Causes
Bacterial Infections
- Bacterial lymphadenitis from lower extremity skin infections, cellulitis, or wounds 5
- Sexually transmitted infections including syphilis, lymphogranuloma venereum, chancroid, and herpes simplex virus 5
Other Infections
- Tuberculosis can cause chronic inguinal lymphadenopathy 5
- Cat scratch disease (Bartonella henselae) from lower extremity scratches 5
Reactive/Inflammatory Causes
Dermatopathic Lymphadenopathy
- Reactive condition in nodes draining areas with chronic skin disruption, including scratch marks from pruritus 6
- Can cause significant enlargement (up to 4 cm) but maintains intact corticohilar border differentiation on ultrasound 6
Non-specific Reactive Hyperplasia
- Most common cause of inguinal lymphadenopathy, accounting for 30-50% of palpable nodes 1
- Results from chronic lower extremity inflammation, minor trauma, or skin conditions 5
Key Diagnostic Features
High-Risk Characteristics Suggesting Malignancy
- Size greater than 2 cm increases malignancy risk 5
- Hard consistency or matted/fused nodes 5
- Fixed to underlying structures (cN3 in penile cancer staging) 2
- Progressive enlargement over 4 weeks 5
- Associated systemic symptoms: fever, night sweats, unintentional weight loss 5
Benign Features
- Intact fatty hilum on ultrasound 2
- Soft, mobile nodes 1
- Bilateral symmetric enlargement (more likely reactive) 5
- Cortical thickness less than 4 mm on ultrasound 2
Diagnostic Algorithm
Initial Clinical Assessment
- Document exact location (superficial vs deep inguinal), number of nodes, size, consistency, mobility, and whether unilateral or bilateral 1
- Examine lower extremities, genitalia, perineum, and anus for primary lesions 2
- Assess for systemic symptoms (fever, night sweats, weight loss) 5
Imaging Evaluation
- Ultrasound with Doppler is the first-line imaging modality 2
Tissue Diagnosis
- Fine-needle aspiration cytology (FNAC) is the standard initial approach with sensitivity 91.7% and specificity 98.2% for malignancy 1
- Ultrasound-guided FNAC increases diagnostic accuracy to 93% sensitivity and 100% specificity when combined with ultrasound findings 2
- Excisional biopsy is indicated when FNAC is negative but clinical suspicion remains high, or when lymphoma is suspected 1, 4
Common Pitfalls
- Overinterpretation of ultrasound findings: Many patients have lymph nodes with atypical features (hilar structural alterations, slight loss of curvature, moderate cortical thickening) that remain stable and benign on follow-up 3
- Premature biopsy of reactive nodes: In patients with obvious lower extremity infections or dermatologic conditions, treat the underlying cause first and reassess in 4 weeks 5
- Underestimating inflammatory causes: Remember that 30-50% of palpable inguinal nodes are inflammatory, even in cancer patients 2, 1
- Avoiding corticosteroids: These can mask lymphoma or other malignancy histologically 5