Scrofuloderma

Definition

Key High-Yield Points at a Glance

Etiology & Pathogenesis

• Causative agent: Mycobacterium tuberculosis (acid-fast bacillus)
• Route: NOT from external inoculation. The bacilli spread per continuitatem (by direct continuity) from an underlying infected focus through the dermis to the skin surface
• Underlying foci (in order of frequency):
  1. Cervical lymph nodes (most common) — classical "scrofula"
  2. Parotid and submandibular lymph nodes
  3. Infected bones/joints (especially sternoclavicular, sternal)
  4. Epididymis, testis
  5. Lacrimal glands
  6. Salivary glands

Clinical Features

Sites

• Neck (most common — overlying cervical lymph nodes) — submandibular, parotid, supraclavicular regions
• Axilla, groin (overlying axillary/inguinal nodes)
• Chest wall (overlying infected ribs/sternum)

Stages of Lesion Progression

1. Stage 1 — Subcutaneous nodule: Firm, painless, skin-colored or bluish subcutaneous nodule; overlying skin initially normal
2. Stage 2 — Softening (fluctuant): Nodule becomes fluctuant (cold abscess) — no warmth, no redness = "cold abscess" (key exam point)
3. Stage 3 — Ulceration: Skin breaks down → irregular, undermined, ragged, violaceous ulcer with bluish-red overhanging edges
4. Stage 4 — Sinus/fistula formation: Multiple discharging sinuses and fistulous tracts with thin, seropurulent or caseous discharge
5. Stage 5 — Healing: Characteristic cord-like, bridge scars (pathognomonic — "bridging scars" or papillomatous scarring)

Exam-Relevant Clinical Points

• Painless (unless secondary bacterial infection)
• Cold abscess (no signs of acute inflammation)
• Undermined/overhanging edges of ulcer
• Bluish-red to violaceous skin discoloration over the lesion
• Characteristic bridging/cord scars on healing — pathognomonic
• Associated systemic TB signs: fever, night sweats, weight loss, malaise

Classic scrofuloderma: ulcerated nodules and plaques in cervical/chest region with fistulous tracts and scarring

Classification of Cutaneous TB (Exam Context)

Diagnosis

1. Mantoux (Tuberculin Skin Test / PPD)

• Strongly positive (>10 mm in immunocompetent; >5 mm in immunocompromised)
• High-grade immunity in scrofuloderma

2. Histopathology (Biopsy — Gold Standard for Morphology)

• Caseating epithelioid granulomas in the dermis
• Langhans giant cells surrounded by epithelioid histiocytes
• Central caseous necrosis
• Peripheral lymphocytic infiltrate

3. Microbiological Investigations

• Ziehl-Neelsen (ZN) stain: AFB (acid-fast bacilli) may be seen in discharge/biopsy — key exam point
• Culture on Lowenstein-Jensen (LJ) medium: Gold standard for confirmation; slow (6–8 weeks)
• CBNAAT/GeneXpert (Nucleic Acid Amplification Test): Rapid molecular diagnosis; also detects rifampicin resistance

4. IGRA (Interferon-Gamma Release Assay)

• QuantiFERON-TB Gold or T-SPOT.TB
• Positive; more specific than Mantoux (no false positives with BCG)

5. Imaging

• Chest X-ray: Look for pulmonary TB (primary focus)
• Ultrasound neck: Assess underlying lymph node involvement, matting, cold abscess
• CT scan: Defines extent of deep tissue involvement

Differential Diagnosis

Treatment

Anti-TB Regimen (Standard WHO/RNTCP/NTEP)

• Total duration: 6 months for cutaneous TB (most forms)
• Some guidelines recommend 9 months if bone/joint involvement coexists
• Daily regimen preferred over intermittent (NTEP, India)

Adjunctive Measures

• Treat underlying focus (lymph node drainage if very large and tense; surgical excision rarely needed)
• Incision and drainage alone is contraindicated — risk of chronic sinus formation and spread
• Nutritional support, address HIV/immunosuppression

Monitoring

• Clinical response (healing of ulcers, closure of sinuses) expected within 2–3 months
• Liver function tests (HRZE are all hepatotoxic — especially INH, RIF, PZA)
• Ophthalmic review if on Ethambutol (ethambutol optic neuropathy)

Prognosis & Complications

• Good prognosis with complete anti-TB therapy
• Residual scarring is universal — characteristic cord/bridge scars
• Complications:
  • Secondary bacterial infection
  • Lymphedema from lymph node destruction
  • Contractures due to extensive fibrosis
  • Marjolin's ulcer (squamous cell carcinoma arising in chronic scrofuloderma scar — rare but important exam point)

High-Yield Mnemonics & Exam Traps

Summary Box (Quick Recall)

Scrofuloderma = Cutaneous TB caused by direct extension (per continuitatem) from underlying TB focus (most commonly cervical lymph nodes) → cold abscess → ulcer with undermined edges → discharging sinuses → heals with bridging cord scars (pathognomonic). Diagnosed by caseating granuloma on histology + AFB on ZN stain. Treated with 2HRZE/4HR.