Panniculitis

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Panniculitis - Fat Under Fire

  • Definition: Inflammation of subcutaneous fat (panniculus adiposus), presenting as deep, tender, erythematous nodules, typically on the lower extremities.
  • Diagnosis: Requires a deep incisional or excisional biopsy for accurate histologic classification, which is crucial for determining the underlying cause and appropriate management.

Erythema Nodosum on Shins

⭐ Erythema nodosum (septal, no vasculitis) is the most common form. It represents a delayed hypersensitivity reaction to various stimuli like infections (Strep), sarcoidosis, IBD, and drugs (OCPs).

Erythema Nodosum - Shins on Fire

  • Pathophysiology: A delayed-type (Type IV) hypersensitivity reaction affecting the septa of subcutaneous fat.
  • Clinical: Presents as tender, erythematous, non-ulcerated nodules, classically on the anterior shins. Fever and arthralgias are common.
  • Histology: Septal panniculitis without primary vasculitis. Early lesions show edema, hemorrhage, and neutrophils; later lesions have lymphocytes, histiocytes, and giant cells, including characteristic Miescher's radial granulomas.
  • Associations:
    • 📌 Mnemonic: ENjoys SODA
      • Sarcoidosis / Streptococcal infection
      • OCPs
      • Drugs (sulfonamides)
      • Autoimmune (e.g., IBD)

⭐ In children, streptococcal infection is the most common trigger, whereas in adults, it's often idiopathic or linked to sarcoidosis.

Differential Diagnosis of Lower Extremity Skin Lesions

Erythema Induratum - Calf Ulcer Attack

  • Pathophysiology: A mostly lobular panniculitis involving a T-cell mediated hypersensitivity reaction, often with vasculitis.
  • Clinical Presentation:
    • Tender, erythematous nodules primarily on the posterior calves.
    • Characteristically ulcerate, drain, and heal with scarring, distinguishing it from erythema nodosum.
  • Histology:
    • Lobular or mixed septal-lobular panniculitis.
    • Necrotizing vasculitis of small to medium-sized vessels within the fat lobules.
  • Associations:
    • Strongly associated with Mycobacterium tuberculosis (scrofuloderma).
    • Also linked to other infections like Nocardia and hepatitis C.

⭐ When linked to tuberculosis, it's termed Bazin's disease. A positive PPD test or IGRA is a key diagnostic clue.

Erythema induratum: clinical presentation and histology

Other Types - The Unusual Suspects

  • Alpha-1-Antitrypsin Deficiency: A lobular panniculitis with liquefactive necrosis, leading to oily discharge and ulceration. Diagnosis requires checking A1AT levels.
  • Factitial Panniculitis: Self-induced by injecting foreign substances (e.g., oils, milk). Presents with bizarre, angular lesions. Histology reveals foreign material.
  • Pancreatic Panniculitis: Lobular type associated with pancreatitis or pancreatic cancer.

    ⭐ Histology classically shows "ghost cells"-anucleated adipocytes with calcified walls from saponification.

Pancreatic Panniculitis Histology

High‑Yield Points - ⚡ Biggest Takeaways

  • Erythema nodosum, the most common form, is a septal panniculitis without vasculitis, typically on the anterior shins.
  • Erythema induratum is a lobular panniculitis with vasculitis, strongly associated with tuberculosis.
  • Pancreatic panniculitis shows ghost-like fat cells from enzymatic fat necrosis due to pancreatitis or carcinoma.
  • Alpha-1 antitrypsin deficiency can cause a neutrophilic lobular panniculitis.
  • Diagnosis requires a deep excisional biopsy to adequately sample the subcutaneous fat.
  • The key histologic distinction is septal versus lobular inflammation.

Practice Questions: Panniculitis

Test your understanding with these related questions

A 55-year-old man is brought to the emergency room by his roommate due to an abdominal pain that started 2 hours ago. His pain is dull, aching, and radiates to the back. He admits to binge drinking alcohol for the past 2 days. Past medical history is significant for multiple admissions to the hospital for similar abdominal pain events, hypertension, and hyperlipidemia. He takes chlorthalidone and atorvastatin. He admits to heavy alcohol consumption over the past 10 years. He has smoked a pack of cigarettes a day for the last 20 years. In the emergency department, his temperature is 38.9℃ (102.0℉), pulse rate is 100/min, and respiratory rate is 28/min. On physical examination, he looks generally unwell and diaphoretic. Auscultation of his heart and lungs reveals an elevated heart rate with a regular rhythm. His lungs are clear to auscultation bilaterally. His abdomen is tympanitic with generalized tenderness. Evaluation of lab values reveals a leukocyte count of 28,000/mm3 with 89% of neutrophils. His amylase level is 255 U/L. A CT scan of the abdomen shows the diffuse enlargement of the pancreas. Which pathological process is most likely occurring in this patient’s peripancreatic tissue?

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Flashcards: Panniculitis

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Which skin cancer typically presents as an elevated nodule with telangiectasias, rolled borders, central crusting, and/or ulcerations? _____

TAP TO REVEAL ANSWER

Which skin cancer typically presents as an elevated nodule with telangiectasias, rolled borders, central crusting, and/or ulcerations? _____

Basal cell carcinoma (nodular type)

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