Panniculitis is inflammation of the subcutaneous fat, the layer of fatty tissue that sits just beneath the skin. It typically shows up as tender, sometimes painful nodules or plaques, most often on the legs, though it can appear nearly anywhere on the body. The term covers a family of conditions rather than a single disease, and figuring out which type of panniculitis someone has is often the key to identifying an underlying cause that ranges from a simple strep infection to pancreatic cancer. That diagnostic detective work is a big part of what makes panniculitis both clinically important and genuinely tricky.
What Panniculitis Looks and Feels Like
The hallmark of panniculitis is subcutaneous nodules, firm lumps that sit below the surface of the skin rather than on it. They are usually tender to the touch, and the overlying skin is often red or dusky. Some forms produce nodules that stay intact and eventually fade, leaving a slight dip or discoloration in the skin. Others ulcerate, breaking through the surface and sometimes draining oily or necrotic material. The nodules tend to appear in crops, meaning several show up over a period of days or weeks, and they can range from a centimeter across to several centimeters.
Location gives doctors an early clue. Nodules clustered on the shins suggest one set of diagnoses, while those on the backs of the calves or thighs suggest another. Panniculitis on the face, arms, or trunk widens the differential considerably. Systemic symptoms like fever, fatigue, joint pain, or muscle aches sometimes accompany the skin findings, and in one reported case of systemic panniculitis (historically called Weber-Christian disease), severe muscle pain was actually the dominant symptom rather than any visible skin change.1Eur Neurol. Myalgia as the major symptom in systemic panniculitis (Weber-Christian disease)
How Doctors Classify It
Subcutaneous fat is organized into lobules separated by thin walls of connective tissue called septa. When inflammation centers on those walls, it is called septal panniculitis. When it targets the fat lobules themselves, it is lobular panniculitis. Each category is further divided by whether blood vessel inflammation (vasculitis) is present.2Indian Journal of Rheumatology. Panniculitis This framework gives pathologists four broad buckets: septal with vasculitis, septal without vasculitis, lobular with vasculitis, and lobular without vasculitis.
In practice, the distinction is rarely perfectly clean. Most cases show some degree of inflammation in both the septa and the lobules, but under the microscope one pattern usually predominates, and that predominant pattern is what guides diagnosis.3PubMed. Panniculitis. Part I. Mostly septal panniculitis A study that examined biopsy specimens across different panniculitis types found that even erythema nodosum, the textbook example of septal panniculitis, frequently showed mixed patterns.4PubMed. Panniculitis: clinical overlap and the significance of biopsy findings So these categories are useful guides, not rigid walls.
Erythema Nodosum, the Most Common Type
If you or someone you know has been told they have panniculitis, the odds favor erythema nodosum (EN). It is the most common form and presents as tender red nodules on the front of the shins, sometimes extending to the ankles or knees. The nodules are usually bilateral and tend to be more uncomfortable than they are dangerous. EN is classified as septal panniculitis without vasculitis, and in many cases it resolves on its own within a few weeks.5PubMed Central. Erythema Nodosum: A Practical Approach and Diagnostic Algorithm
The catch is that EN is often a reaction to something else going on in the body. The most frequently identified triggers include streptococcal throat infections, tuberculosis, sarcoidosis, Behçet disease, inflammatory bowel disease, certain medications, and pregnancy.6PubMed Central. Erythema Nodosum: A Practical Approach and Diagnostic Algorithm In a large share of cases no cause is ever identified, and those are labeled idiopathic. But ruling out an underlying condition before settling on that label is critical, because EN can be the first visible sign of diseases like Crohn’s disease or lymphoma before other symptoms appear.
Treatment for EN itself tends to be supportive: rest, leg elevation, compression stockings, and anti-inflammatory pain relievers. When an underlying trigger is found and treated, the nodules usually resolve along with it.
Nodular Vasculitis and the Tuberculosis Connection
Nodular vasculitis sits on the opposite end of the anatomic spectrum from EN: it is a lobular panniculitis with vasculitis, and its nodules appear on the backs of the calves rather than the shins. The lesions are deeper, can ulcerate, and tend to recur. The condition primarily affects middle-aged women.7Dermatology. Nodular Vasculitis: Retrospective Study of an Uncommon Disease in a Non-Tuberculosis Endemic Country with Focus on Treatment Modalities and Efficacy
When nodular vasculitis is linked to tuberculosis, it goes by the historical name erythema induratum of Bazin. For decades, the assumption was that essentially all cases were tuberculosis-related. That picture has shifted. In countries where TB is uncommon, cases without any evidence of TB infection are increasingly recognized.8PubMed Central. Erythema Induratum (Nodular Vasculitis) of the Lower Extremities Without Tuberculosis in Psoriasis on Secukinumab (Interleukin 17A Inhibition): A Case Report Still, in areas where TB remains prevalent, a study using PCR testing detected Mycobacterium tuberculosis DNA in about three quarters of skin biopsy specimens from patients with lobular granulomatous panniculitis, confirming the link is real even when standard TB tests come back negative.9JAMA Dermatology. Detection of Mycobacterium tuberculosis DNA in Lobular Granulomatous Panniculitis (Erythema Induratum-Nodular Vasculitis)
The practical takeaway: anyone diagnosed with nodular vasculitis should be evaluated for TB, including with advanced testing such as PCR when standard screening is inconclusive. If TB is found, anti-tubercular therapy is the treatment. If TB is ruled out, immunosuppressive therapies may be considered.
Lupus Panniculitis
Lupus can attack the subcutaneous fat in a form called lupus panniculitis (also known as lupus profundus). It shows up as firm, deep nodules or plaques, most commonly on the face and upper arms. Unlike EN nodules, which resolve without scarring, lupus panniculitis can leave behind noticeable depressions in the skin from fat atrophy, which is one of its more distressing features.10PubMed. Clinical entity of Lupus erythematosus panniculitis/lupus erythematosus profundus
The condition affects women far more often than men, with a reported female-to-male ratio of roughly four and a half to one. In one series of 44 patients, the face was the most common site, followed by the upper limbs. Roughly 40 percent of the patients in that series also had systemic lupus, and in most of those cases the panniculitis developed during the course of their existing lupus rather than as its first manifestation.11PubMed. Clinical entity of Lupus erythematosus panniculitis/lupus erythematosus profundus But lupus panniculitis can also occur entirely on its own, without full systemic lupus ever developing.
Under the microscope, it is a lobular panniculitis. What helps distinguish it from other lobular types is the presence of mucin deposits in the surrounding tissue and a heavy lymphocyte-and-plasma-cell infiltrate, along with damage to the skin’s basement membrane zone visible on immunofluorescence testing.12PubMed. Lupus erythematosus panniculitis (lupus profundus): clinical, histopathological, and molecular analysis of nine cases Hydroxychloroquine, the antimalarial drug widely used in lupus, is commonly the first-line systemic therapy.13PubMed Central. Sustained Remission of Lupus Panniculitis Treated With Hydroxychloroquine in a Patient With Crohn’s Disease: A Case Report
Pancreatic Panniculitis
This is one of the more dramatic presentations. Pancreatic panniculitis occurs when enzymes released by a diseased pancreas circulate through the bloodstream and digest subcutaneous fat at distant sites, producing painful nodules that can break down and drain oily material. It develops in up to about three percent of patients with pancreatic disease, including acute or chronic pancreatitis and pancreatic cancer.14PubMed Central. Nonpancreatic Pancreatic Panniculitis: An Incidental Finding in Individuals without Pancreatic Disease? A Case Series and Review of the Literature
The skin lesions sometimes appear before the pancreatic disease is diagnosed, which means unexplained panniculitis with the right biopsy features should prompt a workup of the pancreas, including imaging and enzyme levels. Interestingly, case reports have documented the characteristic microscopic features of pancreatic panniculitis even in patients who have no detectable pancreatic disease at all, raising questions about whether subcutaneous fat necrosis with those specific histologic features is always pancreatic in origin.15PubMed Central. Nonpancreatic Pancreatic Panniculitis: An Incidental Finding in Individuals without Pancreatic Disease? A Case Series and Review of the Literature
Infections as a Cause
The subcutaneous fat can become inflamed by direct infection with bacteria, mycobacteria, or fungi. Infective panniculitis is divided by the type of organism involved: bacterial, mycobacterial, fungal, and, more rarely, viral.16PubMed. Infective panniculitis Staphylococcus aureus is a common culprit among bacterial causes, and atypical mycobacteria (such as Mycobacterium chelonae) can cause panniculitis that is easily mistaken for a non-infectious autoimmune condition.17PubMed. Panniculitis, infection, and dermatomyositis: case and literature review
Infectious panniculitis is especially important to identify quickly because the treatment is antimicrobials, not the immunosuppressive drugs used for autoimmune forms. Giving someone steroids or other immune-suppressing therapy for what turns out to be an infection makes things worse, so tissue cultures from biopsy specimens are a standard part of the workup when infection is on the table.
Cold Panniculitis and Other Physical Triggers
Subcutaneous fat can be injured by physical forces, and the resulting inflammation qualifies as panniculitis. Cold panniculitis is the best-known physical variant. In infants, the subcutaneous fat contains a high proportion of saturated fatty acids that crystallize at relatively mild cold temperatures. When ice packs are applied to a newborn’s skin for medical procedures, firm red plaques can develop at the contact site within a couple of days.18PubMed Central. Cold panniculitis in a newborn due to ice packs in treatment of supraventricular tachycardia Adults occasionally develop cold panniculitis too, though it is far less common because adult fat has a different composition.
Factitial panniculitis results from deliberate or accidental trauma to subcutaneous tissue, such as injection of foreign substances. In one case report, subcutaneous injection of elemental mercury caused a lobular panniculitis with fat necrosis and a dense inflammatory response involving neutrophils, macrophages, and giant cells.19PubMed Central. Factitial panniculitis secondary to injected subcutaneous elemental mercury These cases are rare but important to recognize because the treatment depends entirely on identifying and removing the offending substance.
Panniculitis in Newborns and Children
Subcutaneous fat necrosis of the newborn is a form of panniculitis seen in full-term infants, usually within the first weeks of life. It tends to occur after a stressful birth event such as oxygen deprivation. The condition is generally self-limiting, meaning the nodules resolve on their own, but it can trigger dangerously high calcium levels in the blood. Monitoring for hypercalcemia is essential, and in severe cases treatment with calcitonin or other calcium-lowering agents may be needed.20PubMed Central. Neonatal subcutaneous fat necrosis with hypercalcemia treatment using calcitonin
Cold panniculitis, discussed above, is another pediatric concern given the vulnerability of infant fat to crystallization. Beyond these, children can develop essentially any form of panniculitis that adults get, though some types, like erythema nodosum triggered by strep throat, are particularly common in school-age kids.
Alpha-1 Antitrypsin Deficiency
This genetic condition is best known for causing early-onset lung disease in smokers, but it has a well-established link to panniculitis. Alpha-1 antitrypsin normally acts as a brake on neutrophil enzymes during inflammation. Without enough of it, those enzymes can chew through subcutaneous fat, causing a neutrophilic panniculitis that can be severe and widespread.21PubMed Central. Acute Disseminated Panniculitis Associated with Alpha-1 Antitrypsin Deficiency The skin lesions in alpha-1 antitrypsin deficiency panniculitis can ulcerate and drain oily fluid, and they may be the presenting feature that leads to the underlying diagnosis. Replacement therapy with intravenous alpha-1 antitrypsin concentrate is one treatment avenue in severe cases.
Sclerosing Panniculitis and Chronic Venous Disease
Long-standing problems with blood return from the legs can cause a slowly progressive form of panniculitis known as sclerosing panniculitis (or lipodermatosclerosis). You’ll see it in people with chronic venous insufficiency, where faulty valves in the leg veins lead to persistent swelling, low oxygen levels in the tissue, and eventually fibrosis and hardening of the subcutaneous fat. The lower legs take on a characteristic “inverted champagne bottle” shape, with a tight, woody band around the ankles and calves.22Clinical and Experimental Dermatology. Chronic venous disease. Part 1: pathophysiology and clinical features
Unlike most other panniculitides that present with discrete nodules, sclerosing panniculitis is diffuse. Treatment focuses on the underlying venous disease: compression therapy, leg elevation, exercise to improve calf muscle pumping, and in some cases vein procedures. The condition reinforces a broader point about panniculitis: finding and treating the root cause usually matters more than managing the skin findings alone.
Why Biopsy Matters So Much
Many forms of panniculitis look similar on the surface. Red, tender nodules on the legs could be EN, nodular vasculitis, lupus panniculitis, or something rarer. The microscope is what sorts them out, and getting a good biopsy is not as simple as it sounds. Standard punch biopsies often sample only the superficial skin layers and miss the subcutaneous fat entirely. An adequate panniculitis biopsy requires a deep incisional technique that reaches well into the fat layer.23PubMed. Histopathology of panniculitis–aspects of biopsy techniques and difficulties in diagnosis Specimens should ideally be sent for cultures in addition to standard pathology, because infective panniculitis is one of the main diagnoses that changes treatment completely.
Non-invasive imaging is playing a growing role as a complement to biopsy. High-frequency ultrasound can visualize changes in subcutaneous tissue architecture without cutting, and it has shown value in monitoring disease activity and treatment response in connective tissue panniculitis. CT and MRI offer additional detail, including the ability to detect complications like tissue atrophy or calcium deposits, though these modalities are more expensive and less accessible.24PubMed Central. High-Frequency Ultrasound to Assess Activity in Connective Tissue Panniculitis
When Panniculitis Is Not Really Panniculitis
One of the more serious diagnostic pitfalls is subcutaneous panniculitis-like T-cell lymphoma (SPTCL), a rare cancer that mimics benign panniculitis almost exactly. It presents with deep nodules on the trunk or limbs, and under the microscope it looks like a lobular panniculitis with one critical difference: the cells rimming the fat lobules are atypical T-lymphocytes rather than normal inflammatory cells.25PubMed Central. Subcutaneous Panniculitis-like T-Cell Lymphoma: Diagnostic Challenge and Successful Multimodal Management with Integra® Dermal Matrix—Case Report and Review of the Literature The histologic hallmark is lymphocytes arranged in a ring around individual fat cells, a pattern pathologists call “adipocyte rimming.”
SPTCL can masquerade as panniculitis for months or even years before being correctly identified. Patients may be treated with anti-inflammatory drugs for what is assumed to be a benign condition while a lymphoma smolders. This is one reason why panniculitis that does not respond to expected treatment, keeps recurring, or is accompanied by unexplained fevers, weight loss, or abnormal blood counts warrants a repeat biopsy and careful immunohistochemical analysis.
Rare Genetic Causes
Panniculitis occasionally shows up as part of inherited autoinflammatory syndromes. CANDLE syndrome (Chronic Atypical Neutrophilic Dermatosis with Lipodystrophy and Elevated temperature) is caused by mutations that impair a cellular recycling system called the proteasome. Affected children develop recurrent fevers, characteristic skin lesions including panniculitis, progressive fat loss, and failure to thrive beginning in infancy. The appearance of these children is distinctive enough that experienced clinicians can recognize the syndrome on sight.26PubMed Central. CANDLE Syndrome As a Paradigm of Proteasome-Related Autoinflammation
These monogenic syndromes are exceedingly rare, but they underscore something important about panniculitis more broadly: it is not one disease. It is a pattern of tissue inflammation with dozens of possible causes, and the cause determines everything about the prognosis and treatment. A case of EN from a strep infection resolves in weeks and never recurs once the infection clears. CANDLE syndrome requires lifelong management with targeted immunotherapy. Mistaking one for the other would be a disaster, which is why the careful classification and biopsy approach described above are not just academic exercises but genuinely shape patient outcomes.
Treatment Depends Entirely on the Type
There is no single treatment for panniculitis because there is no single disease. The treatment plan follows the diagnosis:
- EN from infection: treat the infection; the nodules resolve.
- Nodular vasculitis with TB: full anti-tubercular therapy.
- Lupus panniculitis: hydroxychloroquine is a common first-line systemic option, with stronger immunosuppressants like methotrexate or azathioprine for resistant cases.27PubMed Central. Sustained Remission of Lupus Panniculitis Treated With Hydroxychloroquine in a Patient With Crohn’s Disease: A Case Report
- Pancreatic panniculitis: manage the pancreatic disease.
- Alpha-1 antitrypsin deficiency: enzyme replacement in severe cases.
- Sclerosing panniculitis: compression and venous disease management.
- Infective panniculitis: targeted antimicrobials based on culture results.
Across the board, systemic corticosteroids are sometimes used for short-term symptom control in inflammatory forms, but they are a bridge rather than a destination. Topical steroids and calcineurin inhibitors may help with mild, localized disease.28PubMed Central. Sustained Remission of Lupus Panniculitis Treated With Hydroxychloroquine in a Patient With Crohn’s Disease: A Case Report When panniculitis recurs despite appropriate treatment, it often signals either an unresolved underlying trigger or a need to reconsider the diagnosis, including the possibility of SPTCL or another condition that was initially missed.