Panniculitis is a collective term for a group of conditions involving inflammation of the body’s subcutaneous fat layer, which is also known as the panniculus adiposus. This layer of tissue sits directly beneath the skin. When this tissue becomes inflamed, it leads to the formation of noticeable lumps and other symptoms. Identifying the specific type of panniculitis is an important step in determining the correct medical approach.
What Does Panniculitis Look Like? (Symptoms and Presentation)
The hallmark sign of panniculitis is the development of tender, firm nodules or lumps that form deep within the skin. These nodules can vary in size, often measuring several centimeters across, and they are typically painful to the touch. While these lumps can appear almost anywhere on the body, they are most frequently observed on the lower legs, shins, and arms.
The skin overlaying these nodules may exhibit discoloration, ranging from red or purple to a deeper brown, sometimes resembling a bruise. In some forms, the inflamed tissue may undergo necrosis, potentially causing an oily substance to drain from the lesions. As the inflammation resolves, the area may heal with a visible indentation or depression in the skin due to fat loss.
Beyond the localized skin changes, many individuals also experience systemic symptoms that signal a body-wide inflammatory response. These associated symptoms include a general feeling of being unwell, known as malaise, as well as fatigue and fever. Joint pain (arthralgia) and muscle aches are also commonly reported.
Structural Classification of Panniculitis (Septal vs. Lobular)
The subcutaneous fat layer is structurally organized into distinct units, allowing classification based on the precise location of the inflammation. The fat cells are grouped into lobules, and these lobules are separated by bands of connective tissue called septa, which contain blood vessels and nerves. The classification is determined by examining a tissue sample under a microscope.
Septal panniculitis occurs when the inflammation is concentrated primarily within these fibrous septa, often sparing the fat lobules themselves. Erythema nodosum (EN) is the most common example, characterized by inflammation of the septa without damage to the blood vessels. This structural pattern often suggests a reactive process, such as a hypersensitivity reaction to an infection or medication.
Conversely, lobular panniculitis is defined by inflammation that is predominantly contained within the fat lobules. Examples include lupus panniculitis and pancreatic panniculitis, which involves the destruction of fat cells within the lobule. In some lobular types, inflammation of the blood vessels, known as vasculitis, may also be a feature.
Common Triggers and Underlying Causes
The inflammation that characterizes panniculitis is typically a reaction to a wide range of internal and external factors, meaning the condition is often a manifestation of an underlying health issue. The body’s immune response to these factors can trigger the inflammatory cascade in the subcutaneous fat.
One large category of triggers is infectious agents, including bacterial infections like streptococcus or tuberculosis, as well as certain viral, fungal, or parasitic infections. Connective tissue diseases and autoimmune disorders represent another significant group of causes. Systemic conditions such as lupus erythematosus, scleroderma, and inflammatory bowel diseases like Crohn’s disease or ulcerative colitis are known to be associated with various forms of panniculitis.
Specific medications can also induce panniculitis as a side effect, including certain antibiotics, contraceptive pills, and high doses of corticosteroids. Physical factors are another source of inflammation, with trauma, injections into the fat layer, and prolonged exposure to cold temperatures being recognized triggers. Finally, certain systemic disorders like pancreatic diseases, specific types of cancer, and alpha-1 antitrypsin deficiency can all lead to panniculitis.
Diagnosis and Management Approaches
Diagnosing panniculitis requires a thorough medical evaluation that combines the patient’s clinical presentation with laboratory and microscopic evidence. A medical professional will examine the characteristics and location of the nodules, alongside an assessment of any systemic symptoms like fever or joint pain. Blood tests are routinely performed to screen for potential systemic causes, such as infections, autoimmune markers, or indicators of pancreatic disease.
The definitive step in diagnosis and classification is usually a deep incisional skin biopsy, where a section of the inflamed tissue is removed and analyzed. This procedure allows pathologists to determine whether the inflammation is predominantly septal or lobular. Without this histopathological analysis, the clinical similarities between different types can make an accurate diagnosis challenging.
Management of panniculitis is primarily focused on addressing the underlying cause of the inflammation. For many patients, especially those with self-limited forms like erythema nodosum, supportive care is sufficient. This includes rest, elevation of the affected limbs, and the use of nonsteroidal anti-inflammatory drugs (NSAIDs) to alleviate pain and swelling.
If an infectious agent is identified, the appropriate antimicrobial therapy is initiated. When the condition is linked to an autoimmune or systemic disorder, treatment may involve medications that modify the immune response, such as systemic corticosteroids or other immunosuppressive agents. The goal is to control the overactive immune reaction and prevent further damage to the subcutaneous fat.