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Psoriasis Explained

by Jacob Mathew, Jr. DO FACOI FACP CHSE FAWM


Your patient

A 19-year-old woman presents to you with a past medical history significant for joint pain of undetermined etiology in her elbows and knees and a chronic skin rash on her elbows, knees, and trunk. She says that the skin rash has been there for "many years," and it hasn't seemed to respond to over-the-counter steroids that she's purchased at the local pharmacy. She does mention that it seems to improve somewhat when she visits her parents in Florida during the summer over college break. The rash has not spread from its current location along her elbows and knees bilaterally. She works as a camp counselor and is very embarrassed about the appearance and is hoping for a medication to help.

Bottom line, up front

Psoriasis is a chronic and systemic autoimmune inflammatory disease primarily affecting the skin that can be cosmetically disfiguring; an estimated 7.5 million patients in the United States alone suffer from the condition1,2. While a lower incidence is noted in children, it has been increasing as the obesity epidemic increases2. As if the skin involvement were not enough, up to 1/3 of patients will have concurrent musculoskeletal complaints primarily involving the joints, termed psoriatic arthritis, and systemic inflammation leading to disorders like metabolic syndrome, cardiovascular disease, and renal disease to name a few3

So, what is psoriasis?

Psoriasis is a chronic systemic inflammatory condition characterized by well-demarcated erythematous plaques with an overlying silvery white scale; plaques commonly appear on the elbows, knees, scalp, and lower back but can occur elsewhere1. The plaques develop when the life cycle of skin cells accelerates, resulting in the rapid accumulation of rough dead skin cells4. The severity of the cutaneous form of the condition is categorized as localized or generalized, defined by the total amount of skin involvement (see Table 2)5. Up to 1/3 of patients will have other symptoms such as musculoskeletal complaints primarily involving the joints (termed psoriatic arthritis), uveitis, and systemic inflammation leading to metabolic syndrome, cardiovascular disease, and renal disease2,3,6,7. As the severity of the condition increases, the risk of cardiovascular disease increases. Therefore, after making the diagnosis, it is important to consider potential systemic effects and to assess appropriately for cardiovascular disease.

Table 1 - Type of Psoriasis4,8

TypeDescription Comments
PlaqueWell-circumscribed dry, raised, red plaques (generally >0.5 cm in diameter) with overlying silvery scales; lesions may be isolated or generalized.Most common form. May be painful. Occurs anywhere on the body. Can be precipitated by stress, infections, trauma, medications.
ScalpRed pruritic areas with overlying silvery scales near the hairline.One of the most common sites. In children, psoriasis may first appear on the scalp; often localized to the hair line but can extend beyond. Treatments include steroid foams, medicated shampoos, and topical vitamin D.
NailNail pitting with abnormal nail growth and potentially nail discoloration; concomitant onycholysis is common.Often not seen as an isolated presentation but rather coexisting with plaque psoriasis. Involvement of the nails may be a predictor for psoriatic arthritis. Treatment requires topical steroids placed under the nail.
GuttateSmall erythematous papules with a fine silver scale often presenting in an acute manner in a tear-drop shape. Not often as thick as plaque psoriasis. Localized to the trunk, arms, and legs. Look for sparing of the palms and soles.More common in children and younger adults. May be classically triggered by an underlying infection such as group A Streptococcus (GAS).
InverseSmooth patches of red, inflamed skin occurring on the flexural regions such as the armpits, groin, and under breasts. Not known to be thick.Where plaque psoriasis classically occurs on the exterior portions of joints, inverse psoriasis occurs in the flexural regions. Treatment in areas near the genitalia require low-potency topical steroids to avoid skin atrophy.
PustularWidespread or smaller patches that can develop quickly with overlying pus-filled blisters on an erythematous base; may last days to weeks. Often affects the palms and soles.Look for involvement in the hands, fingers, feet, or Achilles region. May require high-potency topical steroids or methotrexate.
ErythrodermicDiffuse, widespread erythema with a peeling quality that can have intense pruritis and burning. Look for concurrent systemic symptoms.Least common of all types; patient may not have any evidence of prior psoriasis leading up to eruption.


Table 2 - Severity Classification of Psoriasis8

SeverityBSA InvolvementFurther ClassificationTreatment Options
Mild<3%Often only a minimal effect on quality of life. Mild erythema, induration, and scaling.Routine skin care, topical therapy.
Moderate3%-10%May be pruritic and/or painful. Locations/extent of disease may cause concern to patient. More erythema and scaling noted.Pharmacologics to include biologic therapy may be indicated.
Severe>10%Disease often cannot be controlled solely with topical therapy. Significant erythema, overlying scales, and induration appreciated.Pharmacologics to include biologic therapy may be indicated.

For reference, 1% body surface area (BSA) is equivalent to the palmar surface of your hand and evaluates specifically the head/neck, upper limbs, trunk, and lower limbs. For more information on determining severity, reference the Psoriasis Area and Severity Index (PASI).9

Table 3 - Spectrum of Psoriasis2,10

CutaneousCommonly occurs on the scalp, extensor portion of the limbs, and gluteal cleft.The most well-known and common form; see description of plaques above.
OcularMay be associated with conjunctivitis, blepharitis, and visual impairment. Ask patients for presence of eye pain and visual disturbances. Consider yearly visual acuity examinations.Seen in up to 2/3 of patients.
NailBoth fingers and toes may be affected; look for nail pitting and thickening. The pathognomonic sign is an "oil stain" on the nail bed.Seen in up to 1/2 of patients with cutaneous psoriasis; high association with psoriatic arthritis.
ArthriticLook for common patterns such as an asymmetric appearance (most common), spinal involvement, and finger involvement.Seen in up to 30% of patients; the cutaneous locations that have highest risk for arthritic involvement are scalp and inguinal. Look for toes specifically to have a "sausage" appearance.


Just to be safe, what else looks like psoriasis?

The differential diagnosis is quite broad and includes atopic and contact dermatitis, lichen planus, pityriasis rosea, and fungal infections. To help distinguish among them, consider the following. Atopic dermatitis is commonly localized to flexural regions and is more pruritic than painful in nature. Contact dermatitis is often associated with an exposure, and there are usually sharply demarcated margins of involvement as well as improvement with cessation of irritant exposure. While lichen planus also presents as plaques, look for an absence of overlying silvery scales; there also may be concomitant mucosal involvement. Pityriasis rosea will classically involve the posterior trunk in a "Christmas tree" distribution. Finally, be aware of fungal infections that can appear similar to psoriasis such as tinea versicolor and tinea corporis; look for risk factors such as recent use of a public facility or close contact with someone with a fungal infection.


How do we treat it?

Psoriasis treatment options have expanded tremendously over the past decade. In general, primary care providers will often defer treatment initiation to dermatologists; however, it is not unreasonable to start therapy in the primary care setting. Based on disease severity (amount of skin involvement), patient preference, and underlying comorbidities, treatment options will vary from topical to oral to biologic (see Table 4). The goal of treatment is to maintain control of the lesions, not necessarily cure them. For localized disease, treatment focuses on topical therapies such as combinations of topical corticosteroids and calcipotriene. Try starting with ointments first before escalating to emollients. For lesions that are unresponsive to this initial therapy, different options are available. If multiple widespread lesions are present, consider increasing sun exposure or starting UVA-UVB therapy. For fixed lesions, intralesional corticosteroid injections can be attempted. Furthermore, consider adding anthralin or tazarotene to the aforementioned topical treatments. If disease starts to be controlled or subsides, then taper off the topical steroids and use them as needed for long-term control during flare-ups. If you are unable to maintain control, consider a referral to a dermatologist.

Despite the more favorable side effect profile associated with topical therapy, systemic therapy has been shown in clinical trials to more effectively reduce clinical symptoms and improve patients' overall quality of life and is more commonly utilized in moderate to severe psoriasis3. Examples of systemic therapy that you or a dermatologist may prescribe include methotrexate, cyclosporine, and acitretin1. If you are the patient's primary care physician, it's important not to feel obligated to start therapy yourself. Instead, focus on the diagnosis and monitoring the patient after treatment has begun (see referral criteria below). If your patient has been started on biologic therapy, routine blood work is often necessary.

Other than pharmacologic therapy, lifestyle measures that the patient can adopt to help keep the disease under control include taking daily baths, avoiding (known) triggers such as stress, and avoiding smoking or being exposed to secondhand smoke.

On the horizon, studies into the role of unsaturated fatty acids hope to determine the role they may (or may not) play in control of psoriasis11. Interestingly, patients with more sunlight exposure are less likely to develop psoriasis because of the antiproliferative effects of sunlight on skin. While this explains the treatment theory behind phototherapy (see table below), patients should not use this as a reason to go outside without sunscreen!

Table 4 - Common Treatment Options for Psoriasis12

  • Emollients - maintain hydration, decrease itching
  • Corticosteroids - anti-inflammatory, antiproliferative, mainstay of topical therapy
  • Vitamin D analogs (tacalcitol and calcipotriene) and vitamin A analog (tazarotene) - can reverse keratinocyte proliferation to help decrease the severity of the plaques

Choice of steroid will depend on the location of skin involvement, thickness of disease, and underlying comorbidities (eg, diabetes).

The combination of vitamin D analogs and highly potent steroids may be more beneficial than either treatment alone.

  • UVB phototherapy
  • UVB phototherapy + acitretin
  • Psoralen plus ultraviolet A (PUVA)
Commonly used in patients with moderate to severe psoriasis due to the antiproliferative and antiinflammatory effects that this light has on plaques. Trials have suggested a mild risk for the development of certain types of skin cancer in patients receiving prolonged phototherapy.13N/A
Systemic (traditional)
  • Acitretin
  • Apremilast
  • Cyclosporin
  • Methotrexate

Acitretin may be associated with mucocutaneous dryness and joint pain. Furthermore, women of childbearing age should not be on this medication.

Methotrexate and cyclosporin are very effective in inducing clinical remission but are more expensive.

LFTs (routinely)




Beta hCG (in females)


Lipid panel



UA (protein)

  • Efalizumab
  • Adalimumab
  • Etanercept
  • Infliximab
Highly effective and well-tolerated treatment that targets activated T-cells; however, more expensive than previous treatment options (approx. 20-25k/year). Patients should have routine blood work (CBC, CMP, and LFTs). Meta-analysis trials suggest infliximab may be the most efficacious of the biologics.



Hepatitis panel


Abbreviations: BUN - blood urea nitrogen; CBC - complete blood count; CMP - comprehensive metabolic panel; hCG - human chorionic gonadotropin; K - potassium; LFTs - liver function tests; Mg - magnesium; N/A - not applicable; sCr - serum creatinine; UA - urinalysis; UV - ultraviolet.

What other conditions should be aware of in my patient with psoriasis?

Remember that psoriasis not only affects the skin but has systemic effects. Understand the risks for joint involvement, behavioral health conditions (such as depression and other mood disorders), cardiovascular disease, and malignancy that can be tied to this condition1,12,14. Furthermore, evidence suggests an increased risk of cardiovascular disease and metabolic syndrome, of which the primary care physician should be aware2. Data suggest we could be doing a better job from this perspective, as only 41% of patients with diagnosed psoriasis receive cardiovascular screening2. Common labs that may be of benefit in patients with diagnosed psoriasis (moderate to severe) include age-appropriate cardiovascular screening such as a lipid panel and hemoglobin A1C as well as height and weight measurements and visual acuity testing.

Besides this, multiple studies have suggested an association between psoriasis and inflammatory bowel disease (IBD) due to a shared inflammatory trigger pathway15. If your patient does have diarrhea (often bloody) that cannot be explained after a workup, consider referral to gastroenterology to rule out IBD. In addition to gastrointestinal conditions, chronic kidney disease is strongly implicated in psoriasis, starting at a young age16. Finally, be aware of commonly used medications in the primary care setting that can lead to a flare (of undiagnosed or diagnosed) psoriasis such as angiotensin-converting enzyme inhibitors, morphine, beta blockers, and penicillin, among others17. This may cause difficulty in managing concurrent cardiovascular disease in patients with previously diagnosed psoriasis.

Our patient revisited

In our 19-year-old patient with isolated patches of psoriasis and concern for psoriatic arthritis, I would consider starting her on topical steroids for her localized lesions. In regard to her arthritis, the area is too vast to discuss further in this review. However, disease-modifying anti-rheumatic drug (DMARD) or anti-tumor necrosis factor (TNF) therapy is often employed. I would recommend referring the patient to a rheumatologist to consider starting one of these treatments. Until she is seen, consider starting naproxen (750-1000 mg/day) or diclofenac (100-150 mg/day) if no contraindications exist14


1. Levine D, Gottlieb A. Evaluation and management of psoriasis: an internist's guide. Med Clin North Am. 2009 Nov;93(6):1291-1303.

2. Bilal J, Malik SU, Riaz IB, Kurtzman DJB. Psoriasis and psoriatic spectrum disease: a primer for the primary care physician. Am J Med. 2018 Oct;131(10);1146-1154.

3. Martin G, Young M, Aldredge L. Recommendations for initiating systemic therapy in patients with psoriasis. J Clin Aesthet Dermatol. 2019 Apr;12(4):13-26.

4. Slide show: Types of psoriasis. Mayo Clinic. Published April 10, 2018. Accessed June 1, 2019.

5. Pardasani AG, Feldman S, Clark AR. Treatment of psoriasis: an algorithm-based approach for prinary care physicians. Am Fam Physician. 2000 Feb 1;61(3):725-733.

6. Langan SM, Seminara NM, Shin DB, et al. Prevalence of metabolic syndrome in patients with psoriasis: a population-based study in the United Kingdom. J Invest Dermatol. 2012 Mar;132(3 Pt 1):556-562.

7. Wan J, Wang S, Haynes K, Denburg MR, Shin DB, Gelfand JM. Risk of moderate to advanced kidney disease in patients with psoriasis: population based cohort study. BMJ. 2013 Oct 15:347:f5961.

8. Kim WB, Jerome D, Yeung J. Diagnosis and management of psoriasis. Can Fam Physician. 2017 Apr;63(4):278-285.

9. Oakley A. PASI score. DermNet NZ. Published 2009. Accessed June 2, 2019.

10. Maddy AJ, Tosti A. What's new in nail disorders. Dermatol Clin. 2019 Apr:37(2):143-147.

11. Honda T, Kabashima K. Current understanding of the role of dietary lipids in the pathophysiology of psoriasis. J Dermatol Sci. 2019 May 21. pii: S09231811(19)301119-7.

12. Armstrong AW, Aldredge L, Yamauchi PS. Managing patients with psoriasis in the busy clinic: practical tips for health care practitioners. J Cutan Med Surg. 2016 May;20(3):196-206.

13. Hearn RMR, Kerr AC, Rahim KF, Ferguson J, Dawe RS. Incidence of skin cancers in 3867 patients treated with narrow-band ultraviolet B phototherapy. Br J Dermatol. 2008 Sep;159(4):931-935.

14. Ritchlin CT, Colbert RA, Gladman DD. Psoriatic arthritis. N Engl J Med. 2017 Mar 9;376(10):957-970.

15. Korman NJ. Management of psoriasis as a systemic disease: what is the evidence? [published online ahead of print June 21, 2019]. Br J Dermatol. doi: 10.1111/bjd.18245.

16. Ungprasert P, Raksasuk S. Psoriasis and risk of incident chronic kidney disease and end-stage renal disease: a systemic review and meta-analysis. Int Urol Nephrol. 2018 Jul;50(7):1277-1283.

17. About psoriasis: causes and triggers. National Psoriasis Foundation. Last reviewed October 23, 2018. Accessed June 25, 2019.





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