What is panniculitis?

Panniculitis: Definition, Classification, and Management

Panniculitis is an inflammation of the subcutaneous fat characterized by tender, erythematous subcutaneous nodules that can be classified into septal or lobular subtypes based on histopathological features. 1, 2

Definition and Clinical Presentation

Panniculitis is characterized by:

• Subcutaneous nodules, typically on the lower extremities
• Both ulcerative and non-ulcerative clinical subtypes
• Tenderness and erythema of affected areas
• Potential association with systemic diseases

Classification

Panniculitis is primarily classified based on histopathological findings:

1. Septal Panniculitis

• Inflammation predominantly affects the fibrous septa of subcutaneous fat
• Types include:
  • With vasculitis:
    • Leukocytoclastic vasculitis
    • Superficial thrombophlebitis
    • Cutaneous polyarteritis nodosa
  • Without vasculitis:
    • Erythema nodosum (most common type)
    • Necrobiosis lipoidica
    • Scleroderma
    • Subcutaneous granuloma annulare
    • Rheumatoid nodule

2. Lobular Panniculitis

• Inflammation predominantly affects the fat lobules
• Types include:
  • With vasculitis:
    • Erythema induratum of Bazin
  • Without vasculitis:
    • Lupus panniculitis
    • Pancreatic panniculitis
    • Alpha-1 antitrypsin deficiency panniculitis
    • Subcutaneous fat necrosis of the newborn
    • Sclerema neonatorum
    • Poststeroid panniculitis
    • Cold panniculitis
    • Infective panniculitis

Diagnostic Approach

A definitive diagnosis requires:

• Deep excisional biopsy with a large amount of tissue for histopathological evaluation 3
• Differentiation between septal and lobular involvement
• Assessment for presence of vasculitis
• Evaluation of inflammatory cell types (lymphocytes, histiocytes, neutrophils)
• Microbiological analysis of biopsy specimen when infection is suspected 2
• T-cell clonal expansion analysis if T-cell lymphoma is suspected 2

Treatment Principles

Treatment depends on the specific type of panniculitis and underlying cause:

General Treatment Approach

1. First-line treatment for most types: Systemic corticosteroids 3

   • Prednisone 1 mg/kg/day (up to 80 mg/day) for 1 month before tapering
   • IV pulse methylprednisolone 500-1000 mg/day for 3-5 days in severe cases
   • Goal: Rapid healing to prevent debilitating outcomes

2. Treatment of underlying conditions:

   • For inflammatory bowel disease-associated panniculitis, treat the underlying IBD 3
   • For alpha-1 antitrypsin deficiency-associated panniculitis, augmentation therapy with purified human AAT or fresh frozen plasma 3

3. Second-line therapies for refractory cases:

   • Immunomodulators (azathioprine)
   • TNF inhibitors (infliximab, adalimumab)
   • Cyclosporine or tacrolimus (oral/IV)
   • Topical tacrolimus for localized cases

Important Clinical Considerations

• Always test for alpha-1 antitrypsin deficiency in biopsy-proven severe panniculitis 3
• Follow patients closely and repeat biopsies if diagnosis remains unclear 2
• Consider autoinflammatory disorders in the differential diagnosis, especially with erythema nodosum 1
• Pediatric panniculitides often require supportive care and management of underlying disorders 4
• Delayed treatment, particularly of pyoderma gangrenosum, can lead to debilitating outcomes 3

Common Pitfalls to Avoid

1. Inadequate biopsy specimen (too small or too superficial)
2. Failure to correlate clinical and histopathological findings
3. Overlooking alpha-1 antitrypsin deficiency
4. Inappropriate steroid use without identifying the specific type of panniculitis
5. Missing underlying systemic diseases that may be causing the panniculitis
6. Confusing subcutaneous panniculitis-like T-cell lymphoma with lupus panniculitis 2

Proper diagnosis and management of panniculitis require a thorough understanding of its various types and their specific treatments to ensure optimal patient outcomes.