Panniculitis
- Lesion
Panniculitis is inflammation of the fat under the skin. It causes tender red lumps, often on the shins.
What it is
Panniculitis is classified by where the inflammation sits in the subcutaneous fat: in the fibrous septa or in the fat lobules, and whether vasculitis is present. Erythema nodosum, the commonest form, is a septal panniculitis that is a reaction to infections, drugs, sarcoidosis, inflammatory bowel disease and pregnancy. Erythema induratum is a lobular panniculitis with vasculitis, classically linked to tuberculosis.
Structure
- Early erythema nodosum: widened, oedematous septa with neutrophils, lymphocytes and eosinophils.
- Later: septal fibrosis, histiocytes and small radial granulomas (Miescher).
- Lobular panniculitis: inflammation within lobules with fat necrosis and lipid-laden macrophages.
Panniculitis by pattern
| Disease | Pattern | Clues |
|---|---|---|
| Erythema nodosum | Septal, no vasculitis | Shins, tender, no ulcer; Miescher granulomas |
| Erythema induratum | Lobular with vasculitis | Calves, ulcerates; tuberculosis |
| Lupus panniculitis | Lobular, lymphocytic | Hyaline fat necrosis, lymphoid follicles |
| Pancreatic panniculitis | Lobular | Ghost adipocytes, saponification, calcium |
| Panniculitis-like T-cell lymphoma | Lobular | Atypical T cells rimming adipocytes |
Clinical notes
- Erythema nodosum prompts a search for streptococcal infection, tuberculosis and sarcoidosis (chest radiograph).
- Erythema nodosum leprosum is a type 2 leprosy reaction, relevant in Colombia and Brazil.
Test yourself
Think of the answer, then tap the question to see it.
What type of panniculitis is erythema nodosum?
A septal panniculitis without vasculitis.
Which infection is classically linked to erythema induratum?
Tuberculosis (a hypersensitivity response to Mycobacterium tuberculosis antigens).
What are three causes of erythema nodosum?
Streptococcal infection, sarcoidosis and inflammatory bowel disease (also tuberculosis, fungi, drugs, pregnancy).
Elsewhere in DurgiPedia
- Granulomatous inflammation: caseating vs non-caseating, the causes to know
- Patterns of necrosis: coagulative, liquefactive, caseous, fat, fibrinoid, gangrenous
- Adipose tissue: white and brown fat
Connections
Educational content on the mechanisms of disease; not a diagnostic or treatment guide and no substitute for a health professional's advice. No doses are given.
Sources: Skin Conditions (MedlinePlus, US National Library of Medicine, 2025).
Spotted a mistake?We are always improving for the community. Tell us what is wrong and our team will review it.Report a mistake
Representative model, for educational purposes only.