panniculitides

Panniculitides are a diverse group of inflammatory disorders that affect the subcutaneous fat, or panniculus. They are classified histologically by whether the inflammation predominantly involves the fat lobules (lobular panniculitis) or the connective tissue septa between lobules (septal panniculitis), and by the presence or absence of vasculitis. This organization helps distinguish diseases and guides evaluation and treatment.

Clinically, panniculitides often present with tender nodules or plaques in the subcutaneous tissue, most commonly on the shins. Erythema nodosum is the prototypical septal panniculitis without vasculitis and typically presents as painful, erythematous nodules that may be accompanied by fever or malaise. Other forms include erythema induratum (nodular vasculitis), a lobular panniculitis with vasculitis that commonly affects the legs and can be recurrent, and lupus panniculitis, a lobular process associated with systemic lupus erythematosus. Pancreatic panniculitis, another form, is linked to pancreatic disease and features fat necrosis related to pancreatic enzymes. A range of infectious, inflammatory, and systemic conditions can underlie panniculitides.

Etiologies are diverse and include infections (e.g., streptococcal), medications (such as oral contraceptives or sulfonamides), autoimmune and systemic diseases (sarcoidosis, inflammatory bowel disease, Behçet disease), malignancy, cold exposure, and occasionally trauma. Diagnosis relies on clinical assessment corroborated by skin biopsy to determine lobular versus septal involvement and to detect vasculitis or fat necrosis. Laboratory workup targets potential underlying causes, including inflammatory markers, infection screens, autoimmune serology, and appropriate imaging if indicated.

Treatment emphasizes addressing the underlying cause and symptom relief. Mild cases may respond to NSAIDs and rest; more persistent or systemic disease may require corticosteroids or immunosuppressants. Prognosis varies by type and associated conditions; erythema nodosum is often self-limited, while other forms may be chronic or recur, and pancreatic panniculitis generally signals significant comorbidity.