The term panniculitis refers to a group of inflammatory disorders in which the primary site of inflammation is in the subcutaneous fat. Suspicion for panniculitis typically first arises from the physical examination.
- Inspection demonstrates a nonspecific area of erythema
- Palpation reveals deep-seated nodules and plaques--characteristic of an inflammatory process located beneath the dermis. Associated tenderness is common.
- Additional features such as ulceration, atrophy, or sclerosis may also be detected and help differentiate the type.
The differential for panniculitis includes:
- Inflammatory disorders:
- Erythema nodosum is the most common (associated itself most commonly with streptococcal pharyngitis, but also classically in IBD and Loefgrens/sarcoidosis)
- lipodermatosclerosis (known as sclerosing panniculitis, related to venous insufficiency)
- lupus panniculitis (related to SLE, associated with atrophy on exam, rare)
- cutaneous vasculitis (including polyarteritis nodosa in our case today, also associated with livedo)
- erythema induratum (presents with ulcers, associated with other infections or drugs)
- Infections: may be caused by bacterial, mycobacterial, fungal, protozoal, or viral infections. Today, we discussed causes of nodular lymphangitis including Sporothrix schenckii, Nocardia, Mycobacterium marinum, leishmaniasis, tularemia, and systemic mycoses
- Trauma: blunt or cold, can also been seen in factitious disorders with subcutaneous injections
- Malignancy: cutaneous lymphoma predominantly
- Deposition: tophi in gout, also calciphylaxis
- Enzymatic destruction: seen in cases of pancreatitis as well as alpha-1 antitrypase deficiency
Note: deep inflammatory nodules and plaques are not exclusive to panniculitis--and disorders involving the deep dermis or fascia may need to be considered (eg. morphea, eosinophilic fasciitis).