Everything you need to know about lupus.

Lupus is defined as a chronic autoimmune disease. This means that the immune system, which is supposed to protect the body, becomes dysregulated and mistakenly attacks its own cells. Its name, derived from the Latin “lupus” for “wolf,” referred in the Middle Ages to destructive facial lesions that were compared to bite marks. The history of its understanding then unfolded step by step, from its first description as a simple skin disease by Pierre CAZENAVE in 1851, to the recognition of its systemic nature by Moriz KAPOSI in 1872. Major discoveries in the 20th century, particularly the detection of specific cells in 1948 and the identification of antibodies targeting these cells in 1954, finally made it possible to change the prognosis of this disease through increasingly targeted treatments.

Far from being a contagious disease, lupus affects both men and women, although there is a striking female predominance , especially during the years of active reproductive function.

Lupus lupus does not present in a uniform way. Its signs vary according to the form of the disease and the organs involved. From an epidemiological standpoint, lupus is still considered a relatively rare disease. Systemic lupus erythematosus has an estimated global prevalence of 4 to 178 cases per 100,000 inhabitants. Its incidence ranges from 0.3 to 23.7 cases, while that of cutaneous forms is 3.9 cases per 100,000 inhabitants.

Systemic lupus erythematosus (SLE).

This is the most common and most complex form, as it can affect several organs simultaneously. The manifestations vary depending on the stages of the disease.

• Joint involvement (90% of cases): Inflammatory pain, often symmetrical, affecting both hands or both wrists, accompanied by morning stiffness.

• Cutaneous manifestations: The best known is the “butterfly-shaped” rash over the cheeks and nose, often triggered by sun exposure.

• Kidney involvement (lupus nephritis): Sometimes silent at first, it can present with high blood pressure or swelling in the ankles. It is one of the most serious complications and requires close, regular laboratory monitoring.

• Neurological and cardiac involvement: These may include cognitive fatigue, headaches, or inflammation of the lining around the heart (pericarditis).

These symptoms may appear in a fluctuating manner, particularly during a lupus flare.

Cutaneous lupus erythematosus (CLE).

In this form, the disease remains confined to the skin. Under the effect of UV rays, certain skin cells are damaged. Normally, the body quietly clears away this cellular debris. In lupus, these cell remnants stagnate at the surface. Antibodies then mistake them for intruders and launch an attack at the boundary between the dermis and the epidermis. It is this localized conflict that causes redness and swelling.

• Discoid lupus: It presents as thick, red, scaly patches (crusts). Because the inflammatory process destroys the deeper layers of the skin, it can leave permanent scars or irreversible hair loss.

• Subacute lupus: It causes red, ring-shaped skin rashes that are highly sensitive to sunlight. Because the inflammation remains more superficial, it does not leave scars.

Drug-induced lupus.

Unlike classic lupus, this form is an “accidental” reaction to certain treatments. These include isoniazid, used in the treatment of tuberculosis, hydralazine, recommended for severe arterial hypertension, and biologic therapies such as TNF-α inhibitors, which are often used to treat Crohn’s disease, rheumatoid arthritis, or psoriasis. It is not a permanent disease, but a transient reaction of the body to a specific molecule that mimics the symptoms of lupus. It usually presents with milder symptoms (fever and joint pain) and resolves after the causative treatment is discontinued.

Neonatal lupus.

This is a rare form of lupus that results from the transfer of maternal antibodies to the fetus. The most common manifestations in newborns are transient skin rashes, although cardiac monitoring is sometimes necessary.

It is important to emphasize that lupus may be diagnosed later in people with Black or darker skin, due to the greater difficulty in recognizing certain skin signs. It is essential that these individuals be better informed about the symptoms of the disease and that they see a physician if warning signs appear, such as skin rashes, joint pain, or unexplained fatigue.

Lupus lupus results from a dysregulation of the immune system. The body can no longer distinguish its own components from exogenous pathogenic agents. This dysfunction stems from a complex genetic predisposition, involving more than one hundred genes associated with this susceptibility. In addition, various environmental and hormonal factors contribute to breaking the body’s immune tolerance.

On this already fragile foundation, external factors such as UV rays or stress act like molecular sparks that activate the innate immune system via specific sensors known as Toll-like receptors. This alarm signal then triggers a massive and disordered production of type I interferons (IFN-I), which form the central pivot of the disease by bridging our immediate defenses and our long-term adaptive immunity.

These interferons, produced in particular by innate lymphoid cells, drive the excessive development and activation of T and B lymphocytes. The collaboration between these cells is further strengthened by a precise molecular connection, the CD40L–CD40 bridge, which prompts B cells to produce autoantibodies on an industrial scale.

In affected individuals, the natural process of removing dead cells, known as apoptosis, is imperfect. As a result, cellular debris accumulates in the body and ultimately comes to be interpreted as dangerous material, creating a self-sustaining cycle. The immune system, constantly stimulated by these warning signals and debris, eventually loses its ability to distinguish the body’s own tissues from foreign elements, thereby triggering the systemic inflammation and organ damage characteristic of lupus.

Hormonal and environmental factors.

Hormones play a major role, particularly estrogens. They promote the activation and survival of certain immune cells, which explains why women are much more affected by this disease. The environment is another key contributing factor. Among the most strongly implicated elements are UV rays, which damage skin cells and massively release inflammatory debris that act as triggers. In addition to sun exposure, tobacco use, intense oxidative stress, and inhalation of industrial pollutants such as silica dust are also involved.

The diagnosis of lupus is based on a stepwise approach, often compared to a true medical investigation. Because of the wide variety of lupus manifestations, no single test is sufficient to establish the diagnosis.

Biological tests for detecting lupus.

The first step generally consists of a blood test to look for antinuclear antibodies (ANA), for which the internationally accepted reference threshold is usually set at a dilution of 1:80. Below this threshold, the probability is low. Above it, especially from 1:160 or 1:320 onward, the signal becomes noisy and it is necessary to look for more specific antibodies, such as anti–double-stranded DNA (anti-dsDNA) or anti-Sm antibodies. For anti–double-stranded DNA antibodies, a level above 7 or 10 IU/mL (depending on the method used) is often considered positive and highly suggestive of an active lupus flare, especially if this value rises rapidly from one month to the next. With regard to anti-Sm antibodies, their mere presence, even at a low level, is a strong marker of lupus. They are almost never found in other diseases. Measurement of complement levels (a group of blood proteins), particularly C3 and C4, is also essential. If C3 falls below 0.80 or 0.90 g/L and C4 below 0.15 g/L, this indicates that the body is consuming its own defense proteins to attack its tissues.

Assessment of organ involvement to refine the diagnosis of lupus.

Targeted tests are performed to detect any possible internal damage. A monitoring of blood creatinine is essential to ensure that the kidneys are healthy. Normal levels range from 60 to 110 µmol/L, or about 0.7 to 1.2 mg/dL. A value that exceeds these limits or rises suddenly may indicate the onset of kidney stress or early kidney dysfunction. The real warning sign often comes from urinalysis. The presence of proteins (proteinuria) above 0.5 g/24 h is the critical threshold suggesting organ dysfunction. If an abnormality is detected, a kidney biopsy may be necessary to assess how severe the disease is. Finally, imaging tests such as MRI or cardiac ultrasound (echocardiography) help ensure that the brain or cardiovascular system are not inflamed.

The diagnosis of lupus photosensitivity.

Among the symptoms, photosensitivity has a special place. It refers to an excessive reaction of the skin to UV radiation. Even brief sun exposure can trigger a characteristic skin rash, and can also cause a more generalized lupus flare. This phenomenon is an important factor in the diagnosis of systemic lupus erythematosus. Unlike a typical sunburn, lupus skin lesions often appear 24 to 48 hours after exposure. In a specialized setting, the tolerance threshold is measured by phototesting. A small area of skin (often on the back) is exposed to increasing doses of UV in order to determine the minimal erythema dose (MED). If the skin reacts to a very low dose that a healthy person’s immune system would ignore, objective photosensitivity is confirmed.

To adjust lupus treatment, physicians do not rely only on the symptoms patients feel. They also use precise tools such as theSLEDAI index (Systemic Lupus Erythematosus Disease Activity Index). This index is used to assess the severity of the disease based on 24 clinical and biological criteria such as organ involvement (kidneys, skin, brain, etc.), laboratory test results, and the presence of specific antibodies.

Each manifestation is assigned a score, ranging from 0 to 105, and the total makes it possible to determine whether the disease is mild, moderate, or highly active. Thresholds are commonly used to distinguish different levels of activity; for example, high disease activity corresponds to a score ≥ 14. This tool is particularly useful for monitoring how the disease evolves over time, assessing the effectiveness of treatments, and adjusting medications according to disease flares. In practice, it helps physicians make more precise decisions to better control the disease, while avoiding unnecessary or excessively intensive treatments.

Today, the management of lupus relies both on controlling lupus flares and on preventing their recurrence.

Preventive measures for living better with lupus.

Even before discussing treatment, certain actions play an essential role in prevention. Sun protection is crucial; it is recommended toapply a sunscreen daily that is both SPF 50+ and broad spectrum (UVA/UVB). Quitting smoking is also strongly recommended, because nicotine and tars are powerful accelerators of metabolism.

These hydrocarbons significantly reduce the effectiveness of certain medications, such as hydroxychloroquine, which is the standard treatment for lupus. By smoking, you trigger overactivity of certain liver enzymes, particularly cytochrome P450 enzymes, which start to break down and eliminate the medication from the body far too quickly. Because the drug no longer has enough time to reach a protective concentration in the blood, skin lesions become harder to stabilize.

Diet is also an important lever. A Mediterranean-type eating pattern, rich in fruits, vegetables, and omega-3 fatty acids, can help reduce inflammation. Careful attention to salt intake is also necessary for patients taking corticosteroids, particularly to prevent hypertension and osteoporosis.

Treatment to control lupus flares.

During a lupus flare, treatment aims to rapidly control inflammation. Nonsteroidal anti-inflammatory drugs (NSAIDs) can relieve mild joint pain. For severe flare-ups, low-dose corticosteroids are used, sometimes given as a direct injection. If a vital organ is affected, immunosuppressive drugs are added to quickly calm the overactive immune system.

Background therapy for lupus.

A long-term maintenance treatment is implemented to stabilize the disease over time. The synthetic antimalarial drugs, such as hydroxychloroquine, are the cornerstone of therapy. They reduce the risk of relapse and provide long-term protection for organs. In some cases, targeted biotherapies such as belimumab are used to act more specifically on the immune system.

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