What is the most likely diagnosis and appropriate diagnostic work‑up for a child with enlarged submandibular lymph nodes and overlying violaceous thinning skin?

Nontuberculous Mycobacterial (NTM) Lymphadenitis

A child presenting with submandibular lymph nodes and overlying violaceous thinning skin most likely has nontuberculous mycobacterial (NTM) lymphadenitis, specifically cervical adenitis caused by Mycobacterium avium complex (MAC).

Most Likely Diagnosis

The clinical presentation described is pathognomonic for NTM lymphadenitis in children. The violaceous discoloration of overlying skin is a hallmark feature that distinguishes NTM infection from other causes of pediatric lymphadenopathy 1, 2. This violaceous skin change occurs as the disease progresses and represents extension of the infection beyond the lymph node capsule 2.

Key Clinical Features Supporting NTM Diagnosis:

• Age: Most commonly affects children 1-5 years old 1
• Location: Submandibular, submaxillary, cervical, or preauricular nodes 1
• Presentation: Insidious onset, typically painless, unilateral (95%), with violaceous skin changes 1, 3, 2
• Natural history: If untreated, progresses to skin ulceration and sinus tract formation with chronic drainage 1, 2
• Duration: Average symptom duration of 4-8 weeks before presentation 3, 2

Causative Organisms:

Currently, approximately 80% of culture-proven NTM lymphadenitis cases are caused by MAC, with the remainder caused by M. scrofulaceum (US/Australia) or M. malmoense and M. haemophilum (Northern Europe/Scandinavia) 1.

Diagnostic Work-Up

Imaging:

Contrast-enhanced CT is the preferred initial imaging modality, showing characteristic findings of peripherally enhancing, centrally cystic lymph nodes with relatively minimal inflammatory stranding of surrounding fat 1, 4. In 10 of 11 patients in one series, this pattern was observed 4.

Laboratory Testing:

1. Skin testing: Purified protein derivative (PPD) testing helps differentiate from tuberculous lymphadenitis. NTM typically shows intermediate reactivity (5-15mm), while tuberculosis shows strong positivity (>15mm) 1

2. Culture: Definitive diagnosis requires culture of excised tissue. Fine needle aspiration has lower yield and risks sinus tract formation 1

Critical Differential Diagnosis:

The most important alternative diagnosis is tuberculous lymphadenitis 1. Key distinguishing features:

• Tuberculosis: More likely with strong PPD positivity (≥15mm), risk factors (foreign-born, positive family history), systemic symptoms, and tender nodes
• NTM: Intermediate PPD reactivity, no systemic symptoms, violaceous skin changes, unilateral presentation

Other considerations include reactive lymphadenopathy from infections, though the violaceous skin changes make this unlikely 5.

Treatment Approach

Excisional surgery without chemotherapy is the recommended treatment for NTM cervical lymphadenitis in children, with a 95% success rate 1.

Surgical Principles:

• Complete excision before suppuration extends beyond the lymph node is ideal 2
• Excision should include involved skin if violaceous changes present 3
• Skin resection with cervicofacial advancement flap may be necessary (performed in 44% of cases in one series) 3

What to Avoid:

• Incisional biopsy alone: Frequently followed by persistent disease, sinus tract formation, and chronic drainage 1
• Anti-TB drugs without macrolide: Ineffective for NTM 1
• Fine needle aspiration as definitive treatment: Risks sinus tract formation 1

Complications to Discuss:

Based on surgical series, inform families of 3:

• Marginal mandibular nerve paresis: 31.8% (most resolve; 35.7% persistent at final follow-up)
• Poor scarring: 20.5%
• Wound infection: 13.6%
• Recurrence: 9.1% (none occurred after complete excision)

Alternative for High-Risk Cases:

For recurrent disease or when surgical risk is high (e.g., facial nerve involvement with preauricular nodes), consider clarithromycin-based multidrug regimen similar to pulmonary MAC treatment 1. However, experience with this approach is limited in pediatric cervical disease.

Special Consideration for Equivocal Cases:

If a child presents with granulomatous disease and strongly positive PPD (≥15mm), initiate anti-TB therapy while awaiting culture results, especially with TB risk factors. Discontinue if cultures are negative and no significant TB risk factors exist 1.