What is panniculitis?
Panniculitis refers to a group of conditions that involve inflammation of subcutaneous fat. Despite having very diverse causes, most forms of panniculitis have the same clinical appearance. The diagnosis is established by a skin biopsy, as there are characteristic microscopic features depending on the cause. The most common form of panniculitis is erythema nodosum.
Panniculitis is classified as mostly septal panniculitis or mostly lobular panniculitis depending on the site of the most intense microscopic inflammation. Most types of panniculitis have both lobular and septal inflammation. Further classification is based on whether or not there is subcutaneous vasculitis.
Classification of panniculitis
Mostly septal panniculitis with vasculitis
Mostly septal panniculitis without vasculitis
- Necrobiosis lipoidica
- Scleroderma, which may be localised (morphoea)
- Subcutaneous granuloma annulare
- Rheumatoid nodule
- Necrobiotic xanthogranuloma
- Erythema nodosum
Mostly lobular panniculitis with vasculitis
- Erythema nodosum leprosum (leprosy)
- Lucio phenomenon
- Idiopathic nodular/lobular panniculitis
- Neutrophilic lobular panniculitis associated with rheumatoid arthritis
- Erythema induratum of Bazin
- Crohn disease
- Nodular vasculitis
Mostly lobular panniculitis without vasculitis
- Sclerosing panniculitis (lipodermatosclerosis)
- Sclerema neonatorum
- Cold panniculitis
- Lupus panniculitis
- Panniculitis in dermatomyositis
- Pancreatic panniculitis
- Alpha-1 antitrypsin deficiency
- Infective panniculitis
- Factitial panniculitis
- Subcutaneous sarcoidosis
- Traumatic panniculitis
- Subcutaneous fat necrosis of the newborn
- Post-steroid panniculitis
- Gout panniculitis
- Crystal-storing panniculitis
- Cytophagic histiocytic panniculitis
- Post-irradiation pseudosclerodermatous panniculitis
- Panniculitis associated with halogenodermas (iodides, bromides)
What are the clinical features of panniculitis?
Panniculitis presents typically with:
- Thickened and firm nodules and plaques
- Erythematous or pigmented overlying skin
- It is often painful or tender
Sometimes, lesions resolve to leave localised subcutaneous atrophy (lipodystrophy).
How is panniculitis diagnosed?
Panniculitis is diagnosed by a combination of clinical features, biopsy findings and microbiological culture. Sometimes other investigations are necessary.
Treatment of panniculitis
Treatment of panniculitis includes:
- Treat the underlying cause, if known (e.g. stop a medication, treat an infection)
- Rest and elevate the affected area
- Compression hosiery (18–25 mm Hg pressure) if these can be tolerated
- Pain relief using anti-inflammatory medications such as aspirin, ibuprofen or diclofenac
- Systemic steroids (oral or injected) to settle the inflammation
- Anti-inflammatory antibiotics including tetracycline or hydroxychloroquine
- Potassium iodide
- Surgical removal of persistent or ulcerated lesions.