A Review of Psoriasis
By Dominique Van De Beest, MS3, UT Southwestern
What is psoriasis and what causes it?
Psoriasis is a chronic inflammatory disorder found in 0.91-8.5% of the population. Although psoriasis is most commonly known as a dermatologic disorder, it is increasingly being recognized as a multi-system inflammatory disease with several extracutaneous comorbidities.
Though the exact cause of psoriasis is unknown, it is clear that genetics combined with environmental triggers predispose to the dysregulation of the immune system that initiates and maintains the disease process. Several genetic loci have been discovered that either predispose to the development of psoriasis, or influence the presentation. A few examples are included in the table below. In psoriasis, it is thought that antigenic stimuli activate innate immune cells in the skin which then produce pro-inflammatory cytokines that attract and activate T-cells. These T-cells then produce cytokines that stimulate keratinocytes to proliferate and produce their own pro-inflammatory cytokines, creating a positive feedback loop. This eventually leads to hyperproliferation and abnormal differentiation of the epidermis that is recognized grossly as erythema and scaling.
|HLA-Cw6||Early-onset psoriasis, guttate psoriasis|
|IL36RN (mutations)||Pustular psoriasis|
Recognizing and diagnosing psoriasis…
The diagnosis of psoriasis is often a clinical one. However, it is important to remember that there are several different forms of psoriasis that greatly differ from the classic plaque psoriasis. Biopsy can be performed if there is doubt in the clinical diagnosis.
The classic presentation is that of plaque psoriasis, which presents with the development of patches of thickened, erythematous plaques or papules with a silvery scale. These lesions can range from a pinpoint papule to greater than 20 cm in diameter. They are typically round to oval in shape and sharply demarcated. These plaques are most commonly symmetrically distributed, and primarily located on the scalp, elbows, knees, and back. They are usually asymptomatic but some complain of pruritus. Other signs that can assist in the physical diagnosis of psoriasis are included below.
|Koebner phenomenon||Skin lesions appearing on lines of trauma.|
|Woronoff’s ring||Lesions are surrounded by a pale, blanching ring.|
|“Signe de la tache de bougie”||On removal of the silver scales, a classic coherence is seen, as if “one scratches on a wax candle”.|
|Auspitz sign||After removal of the silver scale and the surface membrane below, a wet surface will be seen with pinpoint bleedings.|
Forms of psoriasis…
- Plaque psoriasis – Plaque psoriasis is the “classic” appearance of psoriasis (described above). It is the most common form, accounting for approximately 80% of cases in adults. Patients with plaque psoriasis typically present as young adults.
- Guttate psoriasis – Guttate psoriasis presents with the acute appearance of numerous, small psoriatic papules (<1 cm). The papules are mainly located on the trunk. Guttate psoriasis is most common in children and young adults, and has been shown to be strongly associated with recent streptococcal pharyngitis.
- Pustular psoriasis – Pustular psoriasis is a highly dangerous form of psoriasis that can be life-threatening. It is characterized by the acute eruption of widespread erythema, scaling, and pustules with erosions. It is sometimes accompanied by malaise, fever, diarrhea, leukocytosis, and hepatic abnormalities (elevated LFTs). Death can occur from sepsis, hepatic, renal, or pulmonary abnormalities. Patients with pustular psoriasis often have recurrent bouts of the disease, but sometimes a trigger can be found which should be eliminated. During outbreaks, hospitalization may be required.
- Inverse psoriasis – In inverse psoriasis, instead of being located on the extensor surfaces, the lesions are located in the intertriginous areas (ex. inguinal, perineal, intergluteal, axillary, inframammary). Usually, there is no visible scaling, making it easily misdiagnosed as a fungal or bacterial infection.
- Nail psoriasis – Nail psoriasis is often seen as “pitting” that causes the nail to become weak and easily removed. It can also present as a color change of part of the nail to a tan-brown color (“oil drop sign”). Nail psoriasis is often refractory to topical treatments, so systemic treatment is needed. Of note, nail psoriasis can be one of the strongest clinical predictors for coexisting psoriatic arthritis.
- Erythrodermic psoriasis – Erythrodermic is an uncommon, but severe manifestation of psoriasis. It can be recognized by the general erythema and scaling of the skin from head to toe. It can be an acute or chronic process. Patients are at risk for infection because of the loss of adequate cutaneous protection, and for electrolyte abnormalities because of fluid loss. Of note, it is important to consider cutaneous T cell lymphoma as a possible differential diagnosis.
As mentioned above, psoriasis is a complex autoimmune disease that can have multisystem comorbidities. Examples include cardiovascular disease, malignancy, diabetes, inflammatory bowel disease, arthritis, COPD, nonalcoholic fatty liver disease, psychiatric disorders, and infection. A brief discussion of a few of these is below.
- Psoriatic arthritis (PsA) – PsA is an inflammatory arthritis that occurs in 7-42% of patients with psoriasis. A hallmark of PsA is erosive changes of the joints, while serologies remain negative (ex. RF)³. PsA causes asymmetric joint pain and stiffness that is worse in the morning or after periods of immobility, and alleviated by activity. In the majority of cases, the cutaneous symptoms pre-date the arthritis. However, 10-15% will develop arthritis before the cutaneous psoriasis, and another 15% will have undiagnosed cutaneous psoriasis.
The most commonly involved joints are the DIPs and PIPs of the hand and feet. Over time, the affected DIP joints can become fixed in a flexed position. PsA can also affect the spine and sacroiliac joint resulting in a spondylitis/sacroilitis resembling ankylosing spondylitis. Rarely, severe osteolysis leads to a “telescoping” phenomenon which causes the digits to become shorter and wider. This is known as arthritis mutilans.
While it is important to recognize the relation between cutaneous psoriasis and PsA, it is also important to remember that different types of arthritis can occur in people with cutaneous psoriasis. It is therefore, important to remember the different patterns of different types of arthritis and to do serological testing (ex. RF, anti-CCP, ANA, HLA-B27), as well as arthrocentesis with fluid analysis to rule out a septic joint.
- Atherosclerotic disease – Several studies have indicated an increased risk of cardiovascular, cerebrovascular, and peripheral vascular atherosclerotic disease, including an increased risk of death due to these events. The correlation is stronger for patients with severe psoriasis (requiring systemic therapy). Though the reason for this correlation is not completely understood, it is likely that the chronic inflammation responsible for psoriasis is a factor in the development of atherosclerotic disease.
- Malignancy – The highest detected correlation with psoriasis has been with pancreatic cancer. However, other studies have found increased rates of lymphoma (specifically, cutaneous T cell lymphoma and Hodgkin lymphoma). It is possible that this correlation is not due to psoriasis itself, but secondary to immunosuppressive therapies used to treat psoriasis.
Recommendations for evaluation…
The recognition of psoriasis as a chronic, systemic inflammatory condition with multiple comorbidities is essential to the proper treatment of these patients. The following recommendations have been made for the evaluation and treatment of patients with psoriasis.
- 2008 American Journal of Cardiology Editor’s Consensus on Psoriasis and Coronary Artery Disease – The following recommendations have been made for patients with moderate to severe psoriasis.
- Patients should be informed of the potential for increased risk of CAD.
- Patients should be assessed for personal and family history of CAD.
- Annual blood pressure measurements.
- Screenings of lipid profiles and fasting blood glucose.
- Treatment of risk factors for CAD.
- 2008 National Psoriasis Foundation – The following are recommendations for all patients with psoriasis.
- Interventions to diagnose and control depression.
- Monitor and moderate alcohol intake.
- Physicians should be vigilant for signs of lymphoma and other malignancies.
- Age-appropriate screening.
- Annual skin examinations if patients are on immunosuppressive drugs or have been treated with ultraviolet light.
- Routine monitoring for psoriatic arthritis.