Panniculitis · What Is It, Causes, Diagnosis, and More

Panniculitis refers to a group of inflammatory disorders where there is inflammation of the subcutaneous fat layer beneath the skin. Many types of panniculitis have been described, including immune-mediated, infectious, trauma-induced, and malignant, among others. Generally, panniculitis presents as erythematous, inflamed nodules (i.e., solid lesions >10 millimeters in diameter) and plaques (i.e., elevated lesions >1 centimeter) under the dermis, often on the legs and torso. 

Some examples of panniculitides include erythema nodosum, lipodermatosclerosis, lupus panniculitis, and erythema induratum. 

The causes of panniculitis vary and can be divided based on infectious and non-infectious etiologies. Infectious panniculitis can occur secondary to bacterial, mycobacterial, fungal, protozoal, or viral infections. For example, Mycobacterium tuberculosis, the bacteria that causes tuberculosis infection, can result in a skin condition known as erythema induratum.  

Non-infectious etiologies include iatrogenic (e.g., medication induced), autoimmune, rheumatologic, trauma, deposition, enzymatic destruction, and malignancy. Erythema nodosum is one of the most common forms of panniculitis and is associated with preceding streptococcal infection, medications (e.g., oral contraceptives), inflammatory bowel disease (e.g. ulcerative colitis, Crohn’s disease), and malignancy. Lipodermatosclerosis, also known as sclerosing panniculitis, occurs secondary to venous insufficiency, resulting in fibrosis and atrophy of subcutaneous fat. Lupus panniculitis is due to an autoimmune reaction in the deep dermis and adipose tissue. Traumatic panniculitis and cold panniculitis can be caused by blunt trauma and exposure to cold, respectively. Deposition panniculitis includes calciphylaxis which results from the deposition of calcium, and gout which results from the deposition of urate crystals. Pancreatic panniculitis results from increased amounts of pancreatic enzymes (i.e., lipase, amylase) released in the bloodstream and breaking down fat cells within the skin, usually on the upper and lower extremities. Subcutaneous lymphoma is a form of malignancy that can lead to panniculitis. In addition to the above causes, several other conditions may cause panniculitis.  

The signs and symptoms of panniculitis often include inflammatory nodules or plaques located beneath the dermis, typically on the legs, arms, and torso.  

The signs can differ based on the specific cause and subtype of panniculitis. For example, erythema nodosum classically presents with erythematous, tender, non-ulcerated nodules on the anterior lower legs. Lipodermatosclerosis presents with indurated plaques with associated erythema, edema, and hyperpigmentation on the medial aspect of one or both lower legs. Lupus panniculitis presents with erythematous nodules on areas that are often spared in other types of panniculitis, like the upper arms, shoulders, face, scalp, and buttocks. Erythema induratum presents with nodules on the posterior lower legs, often with ulceration.  

Infectious panniculitis lesions can range from small nodules to fluctuant abscesses based on the cause and severity of infection. Panniculitis secondary to trauma presents with tender subcutaneous nodules at the site of injury. Calciphylaxis presents with painful nodules and plaques associated with retiform, or angulated, purpura (i.e., bruising, typically 4-10mm in size, that results due to bleeding under the skin) and necrosis in the thighs and buttocks. Gout typically presents with erythematous, subcutaneous plaques in the lower extremities. Pancreatic panniculitis presents with tender, inflammatory nodules typically on the distal lower extremities that may ulcerate. Acute arthritis is often present with pancreatic panniculitis. Lastly, those with subcutaneous lymphoma typically present with painless nodules or plaques on the extremities, trunk, or face and may have accompanying B symptoms (e.g., unintentional weight loss, fever, night sweats, and fatigue). 

Treatment and prognosis for panniculitis depend on the underlying cause. While some forms of panniculitis can be cured, especially if they are infection-related like erythema induratum, other forms may be chronic and require ongoing supportive treatment, like lupus panniculitis. Erythema nodosum is a self-limiting condition that typically resolves within several weeks without treatment. Lipodermatosclerosis can be treated with lifestyle modifications (e.g., exercise, leg elevation), compression stockings, or topical corticosteroids (e.g., triamcinolone) to the affected area. Lupus panniculitis can be treated with photoprotection through the use of broad-spectrum sunscreens; and medications such as topical or intralesional corticosteroids, and systemic antimalarial agents (e.g., hydroxychloroquine, chloroquine).  

Treatment of erythema induratum may include anti-tuberculosis medications (e.g., isoniazid, ethambutol, rifampicin) if tuberculosis is an underlying cause; and the treatment of infectious panniculitis includes identifying the causative organism and the use of antibiotic medication if warranted. Traumatic panniculitis is usually self-limiting, requiring only symptomatic treatment. Calciphylaxis, pancreatic, and subcutaneous lymphoma are treated by resolving the underlying cause. Generally, corticosteroids, nonsteroidal anti-inflammatory drugs, antimalarials, dapsone, thalidomide, and other immunosuppressive or chemotherapeutic drugs have been used to treat panniculitis. In some cases, treatment might require a multidisciplinary approach involving dermatologists, rheumatologists, and other specialists.