“Ask Dr. HKSH” – Psoriasis

Dr. KUNG Ka Yee

Specialist in Dermatology & Venereology

Q1. What is psoriasis?

Psoriasis is a chronic autoimmune disease. It occurs when the patient’s immune system becomes overactive and mistakenly attacks the body’s own tissues. Immune T cells release excessive amounts of inflammatory cytokines, including tumour necrosis factor-alpha (TNF- α), interleukin (IL)-17 and interleukin (IL)-23. These inflammatory mediators may wrongly target the healthy skin cells, causing inflammation and accelerating the growth of skin cells. This leads to the formation of red plaques on the patient’s skin, covered with the characteristic thick, silvery scales of psoriasis.

Q2. How common is psoriasis?

According to international data, psoriasis affects approximately 2% to 4% of the global population. Local data show lower prevalence at around 0.3%, meaning that approximately 3 in every 1,000 people are living with the condition. Psoriasis affects men and women at similar rates. There are two peak ages of onset: the first is between 15 to 20 years old, and the second is between 45 to 60 years old. Many people develop psoriasis at a relatively young age.

Q3. What causes psoriasis?

Psoriasis is caused by genetic and environmental factors. From a genetic perspective, psoriasis has a well-established hereditary component. Medical research has identified dozens of genetic variants associated with the disease. If either parent has psoriasis, the risk of child developing the condition is approximately 15% to 20%. If both parents have psoriasis, the risk increases to around 40% to 60%. However, inheriting these genetic factors does not necessarily mean that a person will develop psoriasis; it only indicates an increased susceptibility. Psoriasis is often triggered by environmental factors. In fact, more than 70% of people with psoriasis have no clear family history of the condition.

A range of environmental factors may trigger the onset of psoriasis, many of which are closely related to everyday life. These include unhealthy lifestyle habits such as smoking, excessive alcohol consumption, obesity and chronic stress. Certain infections may also act as triggers, particularly streptococcal throat infections (tonsillitis) in children; skin injury, including severe sunburn and excessive scratching. In addition, certain medications, such as some non-steroidal anti-inflammatory drugs (NSAIDs), antihypertensive medications and psychiatric medications, have been associated with triggering psoriasis.

Q4. What are the symptoms of psoriasis?

The signs and symptoms of psoriasis vary with the type of the disease. The first, and also the most common one, is plaque psoriasis. People with plaque psoriasis may develop raised, red plaques with well-defined borders, covered with thick, silvery scales. These plaques usually appear symmetrically, and are most commonly found on the elbows, knees, scalp and trunk.

The second type is guttate psoriasis, which is more common in children and adolescents. It usually occurs after bacterial infection, with numerous small red spots appearing on the trunk. These spots are covered with fine scales. The third type is inverse psoriasis, which is relatively less common. It usually presents as red rashes in skin folds such as the armpits and groin. The last two types are pustular psoriasis and erythrodermic psoriasis. Both are more severe and relatively rare.

Q5. What are the complications of psoriasis?

Based on current medical understanding, psoriasis is not simply a disease that affects the skin and appearance. It is an inflammatory condition that can affect other organs, including the joints and cardiovascular system, as well as metabolism. Around 30% of patients may develop psoriatic arthritis. This can cause joint pain, redness, swelling and also morning stiffness, where one may feel stiffness and discomfort in the joints after waking up, and the discomfort improves with movement. Inflammation may also accelerate the hardening of the arteries, thereby increasing the risk of high blood pressure, heart disease, and stroke. Psoriasis may affect a patient’s metabolism as well, and increase the risk of diabetes, gout and metabolic syndrome.

As psoriasis is an immune-mediated disease, patients are also at increased risk of developing other immune-related conditions, including inflammatory bowel disease, such as Crohn’s disease and uveitis, which affects the eyes. Finally, as  patients may suffer from persistent itching, given the obvious symptoms, about one in four patients may experience depression or anxiety of varying severity, which can affect their studies, work and normal social life.

Q6. What are the treatment options for psoriasis?

Treatment options for psoriasis include topical medications, phototherapy, oral medications and biologic therapies.

Topical medications are suitable for patients with mild to moderate psoriasis. These include topical corticosteroids. To avoid long-term use of steroids, doctors may also prescribe non-steroidal topical treatments, such as TCI medications, vitamin D analogues, coal tar and salicylic acid preparations.

The second option is phototherapy, or light therapy. Doctors use UVA or UVB light to treat the skin, which will help suppress the overactive immune response in the skin. While this is safe and effective, the treatment duration may be relatively long. A single course of treatment usually takes about three to four months, with two to three treatment sessions every week.

Another option is traditional oral medication, namely immunosuppressants, including ciclosporin and methotrexate. These medications are very effective in relieving both skin psoriasis and psoriatic arthritis. However, they are associated with more side effects because, in addition to suppressing the overactive immune system, they also reduce the body’s ability to fight bacterial and viral infections.

Finally, biologic therapy is an effective treatment for psoriasis. Thanks to a better understanding of psoriasis, we now know that the disease is mainly caused by excessive inflammatory cytokines, including the abovementioned tumour necrosis factor-alpha (TNF-α), interleukin (IL)-17 and interleukin (IL)-23. Newer biologic therapies can specifically neutralise or block these inflammatory cytokines, targeting the underlying cause of psoriasis. Unlike traditional oral immunosuppressants, they can help control symptoms without suppressing the immune system.

We also encourage patients to maintain a healthy lifestyle. Patients are advised to stop smoking, avoid excessive alcohol consumption, exercise regularly and maintain a healthy diet to achieve a healthy body weight and enhance both physical and mental well-being. If they need to take medications for other medical conditions, please first consult their doctors to avoid those that may trigger psoriasis.