The Different Types of Psoriasis

Not all appear the same or in the classic location

Psoriasis is not a dermatological condition, as some believe, but rather an autoimmune disorder in which the body's immune system attacks normal cells in the skin. In addition, psoriasis is not just a single disease but a group of different diseases manifesting with distinctive skin symptoms. Even the location of psoriasis lesions can differ from type to type and require different forms of treatment.

To complicate matters even further, you can have several types of psoriasis at once or suddenly switch from one form to another when exposed to different environmental triggers. As an autoimmune disorder, psoriasis requires lifelong surveillance to treat whichever type of disease you have at a given point in time.

Plaque Psoriasis

Plaque psoriasis, also known as psoriasis vulgaris, is the most common form of the disease, accounting for around 80% to 90% of all cases.

Plaque psoriasis is caused when defensive immune cells, called T-cells, suddenly activate in the outer layer of the skin as if an infection has occurred. There, they release inflammatory proteins that accelerate the production of skin cells called keratinocytes. This leads to the build-up of cells on the surface of the skin and the formation of dry, red, flaky plaques.

Psoriatic plaques are most commonly found on the elbows, knees, scalp, and back. The Psoriasis Area and Severity Index (PASI) is often used to categorize the severity of symptoms based on induration (thickness), erythema (redness), desquamation (scaling), and the percentage of skin affected.

The PASI score can help direct the appropriate course of treatment as well as monitor the effectiveness of therapy.

Guttate Psoriasis

Guttate psoriasis is the second most common form of psoriasis. It primarily affects children and, to a lesser degree, adults under 30.

Guttate psoriasis is typically associated with a bacteria or virus that triggers symptoms one to three weeks after infection. The lesions are characteristically small (1 to 10 millimeters in diameter), pink, tear-shaped, and covered with fine scales.

The term guttate is derived from the Latin word gutta, meaning "droplet."

Guttate psoriasis tends to affect children because the diseases known to trigger symptoms occur more frequently in childhood. These include strep throat, chickenpox, and upper respiratory tract infections.

The treatment of guttate psoriasis doesn't vary considerably from that of plaque psoriasis. If a bacterial infection is believed to have triggered an acute event, antibiotics may be used to help control the symptoms.

Inverse Psoriasis

Inverse psoriasis, also known as intertriginous psoriasis, is an uncommon type of psoriasis that affects overweight or obese people more than people of healthy weight. The lesions are usually restricted to skin folds, producing moist rather than dry lesions.

Common areas of involvement include the armpits, under the breasts, between the buttocks, and in the creases of the groin or belly. Inverse psoriasis can be especially problematic when it occurs on the genitals since the skin is so delicate.

Inverse psoriasis is believed to be caused by the excessive accumulation of adipose (fat-storing) cells which release inflammatory proteins, called cytokines, into the surrounding tissues. The greater the accumulation of adipose cells, the greater the inflammation. That, combined with skin-on-skin friction, is believed to trigger the characteristic symptoms.

Weight loss is considered a vital component of inverse psoriasis treatment along with topical and/or oral medications.

Pustular Psoriasis

Pustular psoriasis is characterized by the formation of pus-filled blisters that eventually dry up, leaving splotchy, crusted patches of skin. The causes of pustular psoriasis remain a mystery, although it is believed that sudden and extreme inflammation kills many of the white blood cells involved in the autoimmune assault. (Pus is largely composed of dead white blood cells and a serous fluid known as liquor purus.)

There are several different forms of pustular psoriasis:

  • Localized pustular psoriasis (LPP) is a less severe form of the disease mainly affecting the hands and feet.
  • Generalized pustular psoriasis (GPP), also known as Von Zumbusch psoriasis, can affect large portions of the body, causing potentially life-threatening trauma.
  • Annular pustular psoriasis (APP) occurs in children more than adults and females more than males. It mainly affects the torso, neck, arms, and legs, causing ring-shaped, pus-filled plaques.

The abrupt discontinuation of systemic corticosteroids like prednisone is a common trigger for GPP. Acute upper respiratory tract infections and drugs like terbinafine have also been known to trigger symptoms.

Disease-modifying antirheumatic drugs (DMARDs) like methotrexate or cyclosporine are generally indicated for use alongside other topical or oral anti-inflammatory drugs for the treatment of pustular psoriasis.

Ironically, methotrexate, a drug commonly used to treat psoriasis, can sometimes trigger an adverse reaction, transforming plaque psoriasis into an acute bout of pustular psoriasis.

Scalp Psoriasis

Scalp psoriasis is a form of plaque psoriasis affecting the scalp, forehead, ears, and/or neck.

Scalp psoriasis is often mistaken for seborrheic dermatitis (a.k.a. dandruff). However, scalp psoriasis has more sharply demarcated psoriatic plaques whereas seborrheic dermatitis has ill- defined yellow greasy scales.

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Psoriasis of the scalp
Psoriasis of the scalp. DermNet / CC BY-NC-ND

Even when scalp psoriasis is diagnosed correctly, it can be difficult to treat, as it is difficult to apply topical medications into thick areas of hair. Thicker or more concentrated medications are sometimes needed, along with anti-itch creams and medicated shampoos to prevent secondary fungal infections; intralesional triamcinolone injections at a dermatologist's office can also be helpful.

Nail Psoriasis

Nail psoriasis is a common manifestation of plaque psoriasis. In fact, as many as 90% of people with psoriasis will experience abnormal nail changes at some point in their lives. The fingernails tend to be more affected than the toenails.

Psoriasis can affect all aspects of the nail architecture, causing the pitting, lifting, and crumbling of the nail plate. It may also be recognized by horizontal black lines under the nail (caused by capillary bleeding), white patches on the nail plate, or yellowish-pink spots commonly referred to as "salmon patches" or "oil spots."

Treatment of nail psoriasis involves injections into the matrix (where the nail is generated) or with systemic medications.

Psoriatic Erythroderma

Psoriatic erythroderma is a generalized and severe form of plaque psoriasis affecting all parts of the body. Like Von Zumbusch psoriasis, it can cause the widespread peeling of the skin, leading to rapid dehydration and an increased risk infection. It is also commonly triggered by the abrupt termination of systemic corticosteroids.

If not treated immediately, psoriatic erythroderma can be fatal. Treatment usually involves methotrexate or cyclosporine along with intravenous (IV) antibiotics and fluids to prevent infection and dehydration, respectively.

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By Heather L. Brannon, MD
Heather L. Brannon, MD, is a family practice physician in Mauldin, South Carolina. She has been in practice for over 20 years.