Primary Care Physician Guide to Psoriatic Disease

Introduction

Psoriasis is a very common condition that affects 2% to 3% of the general population worldwide, with more than 7 million individuals in the United States living with the disease. Approximately 30% of patients with psoriasis will develop PsA. Therefore, a primary care physician (PCP) has a good chance of encountering patients with psoriasis and PsA in their practice. Although psoriasis and PsA are typically treated by dermatologists and rheumatologists, PCPs are not uncommonly the primary health care provider for patients with psoriatic disease. One US-based survey has revealed that 30.2% of patients with psoriasis and 28.1% of patients with PsA were primarily treated by a PCP. Furthermore, PCPs play a crucial role in referring patients to specialists - most referrals of patients newly diagnosed with psoriasis or PsA come from PCPs. Even when the primary health care provider for psoriatic disease is a specialist, PCPs have an important role to play in managing the psychosocial component of the disease, screening for common comorbidities of psoriatic disease (including depression, anxiety, inflammatory bowel disease, malignancy, metabolic syndrome and cardiovascular disease), and screening for joint involvement (progression to PsA).

PCPs are thus an important part of a wider network of care for psoriatic disease, which in addition to dermatologists and rheumatologists, may also include psychologists, gastroenterologists, and specialist nurses. However, many PCPs remain insufficiently informed about psoriatic disease and its management. In a survey of Canadian and US PCPs, most reported no or basic knowledge of the indicators of psoriasis to distinguish the disease from other skin conditions (67%), the impact of psoriasis treatment on patient’s existing metabolic conditions like diabetes (85%), the impact of psoriasis treatment on patients with suppressed immune systems (85%), and the efficacy of available treatments for psoriasis (83%). There is therefore a need to educate and support PCPs in the crucial roles they can play in their practice to recognize psoriatic disease, treat or manage it and its associated comorbidities to the extent possible, and, when necessary, refer the patient to the appropriate specialist.

Psoriasis: Clinical Presentation and Diagnosis

The diagnosis of psoriasis is typically clinical, as no specific laboratory tests exist. Although it is a heterogeneous disease which can affect joints, nails, eyes, and the cardiovascular system, psoriasis mainly manifests on the skin. Erythematous and scaly skin lesions (Figure 4-1) characterize plaque psoriasis — the most common (80%) form of psoriasis — and are the classic feature on which diagnosis is based. However, PCPs should be aware that other cutaneous manifestations of psoriasis exist, including guttate, palmar-plantar, pustular and erythrodermic psoriasis.

Guttate psoriasis is characterized by a large number of small plaques which are distributed diffusely over the trunk and extremities (Figure 4-3). Two subtypes are distinguished based on the developmental course of the disease - in small plaque psoriasis, the lesions develop slowly, while in guttate syndrome, they occur suddenly, often triggered by infection. Palmar-plantar psoriasis manifests on the palms (Figure 4-4) and soles (Figure 4-5), which makes it limited in area but often devastating to the patient. Pustular psoriasis is characterized by lesions containing small, white pustules that can be painful (Figure 4-8). It can be localized or generalized, with the latter form either erupting suddenly (Figure 4-7) or developing over time. Finally, erythrodermic psoriasis is extensive (covering more than 80% of the body surface area [BSA]), and characterized by plaques of deeper red color and finer scales than typical plaque psoriasis (Figure 4-9).

Psoriatic lesions with distinguishing characteristics can occur in specific locations, including skin folds (inverse psoriasis), the face, the genitals, and the nails. The appearance of inverse and facial psoriasis typically differs from plaque psoriasis because lesional borders are often less distinct and, in cases of local yeast superinfection, there may be small satellite lesions present. Because of the increased moisture in areas of inverse and genital psoriasis, scale is typically milder, finer, and has a waxy appearance (Figure 4-10). Finally, psoriasis often (~40% of cases) involves the nails. There are two main aspects of nail psoriasis: 1) the involvement of nail matrix which causes changes in the nail plate, including pits and deformities (Figure 4-11); and 2) involvement of the nail bed, which causes visible changes such as discoloration under the nail or detachment of the nail (onycholysis). One pathognomonic feature of nail psoriasis are oil-stain-like patches, which distinguish it from a fungal infection.

A number of conditions have features reminiscent of psoriasis, including atopic dermatitis (eczema), lichen planus (a chronic inflammatory disease), pityriasis rosea (diffuse rash of sudden onset and putative viral origin), tinea corporis (fungal infection), and onychomycosis (fungal infection of the nails). The distinguishing clinical features of these conditions are listed in Table 15-1.

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Psoriatic Arthritis: Clinical Presentation, Screening, and Diagnosis

Psoriatic arthritis is a form of arthritis (joint inflammation) associated with psoriasis. It is characterized by synovitis (inflammation of the synovial membrane that lines the joints), enthesitis (inflammation of entheses, the sites of tendon or ligament insertion into bone), dactylitis (inflammation of fingers or toes) and spondylitis (inflammation of the vertebrae).1 Nail abnormalities, including pitting, oil spots, and frank onycholysis, are even more common in PsA than in psoriasis (~80% of cases). There are five classical subgroups of PsA, depending on the pattern of joint involvement: 1) asymmetric oligoarthritis; 2) symmetric polyarthritis; 3) arthritis predominantly involving distal interphalangeal (DIP) joints; 4) arthritis mutilans; and 5) predominantly axial spondyloarthropathy (Table 2-1). It is important to note that patients may have more than one subtype of PsA at the same time.

Asymmetric oligoarthritis is the most common pattern of PsA. It is characterized by scattered involvement (erythema and swelling) of DIP, proximal interphalangeal (PIP), and metatarsophalangeal (MTP) joints; patients with dactylitis fall into this subtype (Figure 3-1). Symmetrical polyarthritis is characterized by a pattern similar to rheumatoid arthritis, including extensive, symmetrical small joint involvement (Figure 3-2) As the name suggests, arthritis predominantly involving DIP is characterized by the presence of significant DIP synovitis (Figure 3-3) nail changes are also often present. Arthritis mutilans is a rare but especially disfiguring form of PsA. In this subtype, osteolysis of the phalanges causes disintegration and resorption of the joints, resulting in digit shortening and malformation (Figure 3-6)). Finally, predominantly axial spondyloarthropathy is another relatively rare subtype of PsA. It can be difficult to distinguish from ankylosing spondylitis with comorbid psoriasis. It is characterized by inflammatory back pain, which can be distinguished from degenerative arthritis or musculoskeletal back pain by the presence of stiffness in the morning or after pro¬longed inactivity, and by the improvement of pain with activity. Radiographic changes may be present in the spine (Figure 3-5)

Currently, the most widely used classification scheme for PsA is Classification of Psoriatic Arthritis (CASPAR). The CASPAR criteria were developed by an international group, which used several existing classification schemes and added new criteria. The criteria include five categories (Table 2-2): 1) psoriasis (current, personal history or family history); 2) psoriatic nail dystrophy; 3) negative test for rheumatoid factor (RF); 4) dactylitis (current or history); and 5) radiologic evidence of juxta-articular new bone formation. The presence of any of these criteria adds one point to the total score, with the exception of current psoriasis, which adds two points. A disease is classified as PsA if the point total is three or higher. It is important to note that the CASPAR criteria can only be applied in cases where there is established inflammatory articular disease (joint, spine or entheseal).

Establishing a diagnosis of PsA can be challenging since, like for psoriasis, no specific laboratory tests exist. Diagnosis depends on a combination of patient history (including the CASPAR criteria), clinical exam (evaluation of the joints, entheses, spine, and nails), laboratory findings (eg, presence or absence of RF) and imaging (eg, radiographs of affected joints). Several inflammatory and non-inflammatory conditions resemble PsA and are important to consider as differential diagnoses (Table 2-3). These include osteoarthritis, gout, rheumatoid arthritis, reactive arthritis, arthritis associated with inflammatory bowel disease and ankylosing spondylitis.

It is important to remember that PsA most often develops in patients with pre-existing psoriasis. PsA typically develops within five to 10 years of the onset of cutaneous disease. Thus, screening psoriasis patients for possible joint involvement is an important part of psoriatic disease management by PCPs. However, PCPs should also be aware that an estimated 10% of patients will develop PsA before any skin disease, and that PsA should therefore be considered whenever there is joint inflammation.

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Management of Psoriatic Disease

The treatment of psoriatic disease should be individualized on the basis of patient preferences, the impact of the disease on quality of life, and the risk-benefit profile of the chosen therapy. PCPs can meaningfully contribute to the main treatment goals, including both the reduction of lesion size and joint inflammation, and the improvement of quality of life.

Treatment of Psoriasis

A number of effective treatment modalities exist for psoriasis. Options include topical agents (emollients, topical corticosteroids, tar and anthralin and vitamin D analogues), systemic nonbiologic agents (methotrexate, acitretin, cyclosporin and apremilast), and systemic biologic agents (the anti-TNF agents etanercept, infliximab, adalimumab and certolizumab; the anti-IL-12/23 drug ustekinumab; the anti-IL-17 agents secukinumab, ixekizumab and brodalumab; and the anti-IL-23 drugs guselkumab, tildrakizumab and risankizumab).

The choice of therapy depends on disease extent; mild disease (<5% BSA) is typically treated by topical agents, while moderate to severe psoriasis may require the use of systemic agents. The use of biologics as monotherapy for the treatment of moderate to severe psoriasis has revolutionized the field, and their use by PCPs may be warranted. In addition to pharmacological treatment, PCPs can play a role in psoriasis treatment by encouraging behavioral changes such as weight loss, smoking cessation and adoption of a healthy diet and lifestyle, all of which can decrease disease activity and lead to significant improvements in quality of life.

Treatment of PsA

Like for psoriasis, the pharmacological treatment armamentarium for PsA is broad, although by nature of the disease largely limited to systemic agents. Available options include nonbiologic agents (nonsteroidal anti-inflammatory drugs [NSAIDs], corticosteroids, disease-modifying anti-rheumatic drugs [DMARDs], methotrexate, apremilast and the JAK inhibitors tofacitinib and upadacitinib), anti-TNF agents (etanercept, infliximab, adalimumab, golimumab and certolizumab), and other biologic agents (ustekinumab, risankizumab, secukinumab, ixekizumab, brodalumab and abatacept, among others).

Patients with PsA should in general be referred to a rheumatologist for treatment. However, PCPs can prescribe NSAIDs or, depending on their level of comfort and knowledge, even other systemic agents. PCPs can also refer the patient to a physiotherapist, which can form the first-line or adjunctive treatment for certain PsA subtypes (especially those involving axial disease and enthesitis).

Screening for and Managing Comorbidities

Patients with psoriatic disease have a higher risk of developing a number of comorbidities, including depression, anxiety, inflammatory bowel disease, certain malignancies, cardiometabolic disease and chronic renal disease. The role of the PCP therefore extends beyond focusing on the treatment of psoriatic disease itself to screen for and provide timely management of associated conditions.

Depression and Anxiety

Psychiatric comorbidities, particularly depression and anxiety, are extremely common in patients with psoriasis. PCPs and other health care providers can help assess psychiatric comorbidities through both clinical judgment and the use of screening questionnaires such as the patient health questionnaire (PHQ) 9 and generalized anxiety disorder scale (GAD) 7. Patients with depression or mood disorders can be directed to online resources, including the National Psoriasis Foundation (NPF) website, for additional information on how to cope with psychiatric comorbidities. However, patients with depression or anxiety should be also referred to a psychiatrist for treatment.

Psychosocial Impact

Psoriatic disease is also associated with significant psychosocial burden, which is the result of disease stigma. Misconceptions about psoriasis include the belief that it is contagious and that it is related to poor personal hygiene. Discriminatory behavior toward patients with psoriasis is common, as is low self-esteem among the patients themselves. PCPs can offer support and information to patients and friends or family members, introduce patients to external resources such as the NPF website, and encourage patients to join support groups or family therapy.

Inflammatory Bowel Disease (IBD)

Multiple studies have found a link between psoriatic disease and IBD, particularly Crohn’s disease. The two diseases share a mechanistic link in the dysregulation of mediators of inflammation such as TNFα and IL-12/23. PCPs should be aware of this association, as screening for any relevant patient history and performing a physical examination increases the chances of detecting IBD early in patients with psoriatic disease.

Malignancy

In a large meta-analysis of 112 studies and more than 2 million patients, psoriasis was associated with increased risk of keratinocyte cancer and lymphomas (and a slightly increased overall risk of cancer). Because of the suspected link between the immunomodulating biologics used for psoriasis treatment and lymphoma development, PCPs treating psoriasis patients need to be aware of the increased risk, although further research is needed to determine if the association is real.

Cardiometabolic Disease

Psoriasis has been linked with a large spectrum of cardiometabolic diseases, including myocardial infarction, stroke, dyslipidemia, peripheral vascular disease, metabolic syndrome and type 2 diabetes. It has been proposed that atherosclerotic disease and psoriatic disease share a common mechanistic cause in the upregulation of proinflammatory helper T cells. PCPs can help reduce the risk of cardiometabolic disease in patients with psoriasis by monitoring their blood pressure, BMI, waist circumference, fasting serum lipoprotein and high-density lipoprotein, and fasting blood glucose. Encouraging smoking cessation and weight loss is another strategy PCPs can adopt, since smoking and obesity are linked to both psoriasis and cardiometabolic disease.

Kidney Disease

A strong association between psoriasis and chronic kidney disease has been observed in several studies. Mechanistically, the inflammatory changes that drive psoriatic disease may also damage the renal microvasculature, leading to decreased kidney function. PCPs should monitor kidney function in patients with psoriasis affecting more than 3% of BSA. The use of drugs associated with nephrotoxicity (such as cyclosporine) should be considered with care in patients with moderate or severe psoriasis.

Referral to a Specialist

Despite the important role PCPs can play in screening for, diagnosing and managing psoriatic disease, in certain cases (particularly with severe disease) it is necessary to triage and refer patients to a dermatologist and/or rheumatologist for specialty care.

Referral to a Dermatologist

When to refer a patient with psoriasis to a dermatologist largely depends on the individual PCP’s comfort level in managing the patient’s disease. Mild disease should be within the comfort zone of most PCPs. It has been suggested that referral to a dermatologist is warranted if the patient is not responding to initial therapy, or if psoriatic lesions cover more than 5% to 10% of the patient’s BSA. Referral to a dermatologist or another specialist may also be required in cases of numerous comorbidities and polypharmacy, for example in elderly patients. Additional reasons for referral to a dermatologist have been suggested and are presented in Table 15-2.

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Referral to a Rheumatologist

In general, a referral to a rheumatologist is warranted as soon as PsA is diagnosed or suspected. Therefore, the most important role of the PCP is to identify PsA. In addition to the signs and symptoms of PsA and the CASPAR criteria discussed earlier, a set of four simple questions initially developed to help dermatologists identify patients with PsA may be useful to PCPs. These questions include:

• Do you have a history of joint pain or swelling?
• Do you have stiffness in the morning?
• Have you had X-rays taken of your joints?
• Do you have psoriatic arthritis?

While waiting for the rheumatological review, PCPs can prescribe NSAIDs to relieve joint pain in patients with suspected or diagnosed PsA.

Referral to Other Specialists

If the PCP comes to suspect psychiatric comorbidities such as depression or anxiety, a referral to a psychiatrist for treatment with selective serotonin reuptake inhibitors and cognitive behavioral therapy is warranted. If the patient complains of eye pain, loss of visual acuity, or blurry vision, symptoms not uncommon in ocular complications associated with psoriasis (conjunctivitis, blepharitis, xerophthalmia and uveitis), they should urgently be referred to an ophthalmologist.