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, malfunctions and mistakenly attacks its own cells. Its name, derived from the Latin “lupus” meaning “wolf”, referred in the Middle Ages to destructive facial lesions likened to bite marks. The history of its understanding then developed 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, notably the identification of specific cells in 1948 and of the antibodies targeting these cells in 1954, finally made it possible to transform the prognosis of this disease thanks to increasingly targeted treatments.

Far from being a contagious disease, lupus affects both men and women, although there is a marked female predominance , particularly during their reproductive years.

Lupus lupus does not present in a uniform manner. Its manifestations vary according to the form of the disease and the organs involved. From an epidemiological perspective, lupus remains 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, whereas that of cutaneous forms is 3.9 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 according to the phases 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 on the cheeks and nose, often triggered by sunlight.

• Renal involvement (lupus nephritis): Sometimes silent at the onset, it manifests as high blood pressure or swelling of the ankles. It is one of the most serious complications and requires strict biological monitoring.

• Neurological and cardiac manifestations: These may include cognitive fatigue, headaches, or inflammation of the membrane surrounding the heart (pericarditis).

These manifestations 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 altered. Normally, the body discreetly clears away this debris. In lupus, these cellular residues accumulate on the surface. Antibodies then mistake them for intruders and launch an attack at the boundary between the dermis and the epidermis. It is this localised conflict that causes redness and swelling.

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

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

Drug‑induced lupus.

Unlike classical 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 biotherapies such as TNF-α inhibitors, which are frequently used in the treatment of 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 generally manifests as milder symptoms (fever and joint pain) and resolves after the offending treatment is discontinued.

Neonatal lupus.

This is a rare form of lupus, resulting from the transfer of maternal antibodies to the foetus. The most common manifestations in the newborn are transient skin rashes, although cardiac monitoring is sometimes required.

It is important to emphasise that the diagnosis of lupus may be made later in people with black skin, due to the difficulty of identifying certain cutaneous signs. It is essential that these individuals are better informed about the symptoms of the disease and that they consult a doctor if they notice warning signs, such as skin rashes, joint pain or unexplained fatigue.

Lupus lupus results from a dysregulation of the immune system. The body is no longer able to distinguish its own constituents from exogenous pathogenic agents. This dysfunction arises from a complex genetic predisposition, linked to more than one hundred genes involved in this susceptibility. In addition, various environmental and hormonal factors contribute to breaking the immune tolerance of the body.

On this already fragile ground, 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 defences and our long-term adaptive immunity.

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

In affected individuals, the natural process of eliminating dead cells, known as apoptosis, is imperfect. Cellular debris then accumulates within the body and eventually comes to be interpreted as dangerous, and this cycle perpetuates itself. The immune system, relentlessly stimulated by these warning signals and debris, ultimately loses its ability to distinguish its own tissues from foreign ones, thereby triggering the systemic inflammation and organ damage characteristic of lupus.

Hormonal and environmental factors.

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

The diagnosis of lupus is based on a stepwise approach, often likened to a genuine medical investigation. Owing to the wide range of lupus manifestations, no single test is sufficient to establish the diagnosis.

Biological tests for detecting lupus.

The first step generally involves 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 likelihood is low. Above it, particularly from 1/160 or 1/320, the signal becomes noisy and makes it necessary to look for more specific antibodies, such as anti–double-stranded DNA (native anti-DNA) or anti-Sm antibodies. For native anti-DNA antibodies, a level above 7 or 10 IU/mL (depending on the method used) is often considered positive and highly suggestive of a 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. The measurement of complement (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 means that the body is using its own defence mechanisms to attack its tissues.

Assessing organ involvement to complete the diagnosis of lupus.

Targeted examinations are carried out in order to detect any possible internal involvement. A monitoring of blood creatinine is essential to ensure that the kidneys are healthy. Its normal level is between 60 and 110 µmol/L, i.e. approximately 0.7 to 1.2 mg/dL. A value that exceeds these limits or rises abruptly may indicate the onset of renal impairment. The real warning sign often comes from urine analysis. The presence of proteins (proteinuria) exceeding 0.5 g/24 h is the critical threshold suggesting organ dysfunction. If an abnormality is detected, a kidney biopsy may be required to assess the severity of the disease. Finally, investigations such as MRI or heart ultrasound (echocardiography) make it possible to ensure that the brain or cardiovascular system are not inflamed.

The diagnosis of lupus photosensitivity.

Among the symptoms, photosensitivity occupies a particular place. It corresponds to an excessive reaction of the skin to UV rays. Simple exposure to sunlight can trigger a characteristic skin rash, but can also induce a more general flare of lupus. This phenomenon is moreover an important element in the diagnosis of systemic lupus erythematosus. Unlike an ordinary sunburn, the lupus lesion often appears 24 to 48 hours after exposure. In a specialist 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 the immune system of a healthy person would ignore, objective photosensitivity is confirmed.

To tailor lupus treatment, doctors do not rely solely on the symptoms reported by the patient. They also use precise tools such as theSLEDAI index (Systemic Lupus Erythematosus Disease Activity Index). This index makes it possible to assess the severity of the disease using 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 associated with 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 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 flare‑ups. In practice, it helps clinicians to make more precise decisions to achieve better disease control, while avoiding unnecessary or excessively burdensome 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 measures play an essential role in prevention. Protection against the sun is crucial; it is recommended toapply a sunscreen daily that is both SPF 50+ and broad spectrum (UVA/UVB). Stopping smoking is also strongly recommended, as nicotine and tar are powerful accelerators of metabolism.

These hydrocarbons significantly reduce the effectiveness of certain medications, such as hydroxychloroquine, which is the first-line treatment for lupus. By smoking, you trigger an overactivity of certain liver enzymes, particularly cytochromes P450, which start to break down and eliminate the drug far too quickly from the body. As the medication no longer has time to reach a protective concentration in the blood, skin lesions become more difficult to stabilise.

Diet is also an important lever. A Mediterranean-type diet, rich in fruit, vegetables and omega-3, can help to reduce inflammation. Particular attention to salt intake is also necessary in patients on corticosteroids, notably to prevent hypertension and osteoporosis.

Treatment to control lupus flare-ups.

During a lupus flare, treatment aims to rapidly control inflammation. Non‑steroidal anti‑inflammatory drugs (NSAIDs) can relieve mild joint pain. For severe flares, low‑dose corticosteroids are used, sometimes given by direct injection. If a vital organ is affected, immunosuppressants are added to dampen the immune system very quickly.

Background treatment of lupus.

Background therapy is instituted to stabilise the disease over the long term. The synthetic antimalarial drugs, such as hydroxychloroquine, form the cornerstone of treatment. They reduce the risk of relapse and provide long-term protection for the organs. In certain cases, targeted biotherapies such as belimumab are used to act more specifically on the immune system.

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