The Role of the Dermatologist in Identification and Treatment of the Early Stages of Psoriatic Arthritis

I. Landells, MD, FRCPC^1,2; C. MacCallum, BSc Pharm¹; M. Khraishi, MD, FRCPC1,²

¹Memorial University of Newfoundland Faculty of Medicine, St. John’s, NL, Canada
²Nexus Clinical Research, St. John’s, NL, Canada

ABSTRACT

Early diagnosis of psoriatic arthritis (PsA) is essential for preventing disease progression and joint destruction. The majority of patients develop PsA years after the onset of their skin disease. Therefore, dermatologists are in a strategic position to make the diagnosis of PsA, and either manage it or refer the patient to a rheumatologist in order to prevent the potentially irreversible destruction of the affected joints. We will review the presentation and temporal relationship of psoriasis and PsA, the diagnosis, classification, and management, in addition to the role of the dermatologist in the early detection of PsA.

Key Words:
Distal interphalangeal joint (DIP), metatarsophalangeal joint (MTP), psoriasis, psoriatic arthritis, PsA

Psoriatic arthritis (PsA) is often described as a chronic, inflammatory arthropathy affecting the distal interphalangeal joints (DIP) of the hands, metatarsophalangeal joints (MTP)
of the feet, and spine in association with psoriasis.1 One to three percent of the world population has been diagnosed with psoriasis.²

Estimates of the prevalence of PsA within the psoriasis population range from 6%-39%.3 The Psoriasis Foundation 2001 Benchmark Survey estimated the prevalence of PsA in patients with psoriasis to be as high as 23%.⁴ PsA is often under diagnosed or misdiagnosed, and therefore, statistics may be misrepresented.

Clinical Presentation

There appears to be great variability in the case definition for PsA. One such definition, proposed by Moll and Wright, defines PsA as “an inflammatory arthritis associated with
psoriasis and usually with a negative serological test for rheumatoid arthritis.”⁵ Due to the broad spectrum of PsA there has been a need to create subgroups (Table 1).

Characteristic features of psoriatic arthritis include: swelling, erythema, warmth, and inflammation of the affected joint. PsA can present with asymmetrical joint distribution,
involving more joints over time and progressing as an oligoarticular/polyarticular disease. Almost any joint can be involved including peripheral (e.g., the DIPs) and/ or axial joints (e.g., spine and sacroiliac joints). PsA can also manifest with involvement of periarticular structures such as tenosynovitis (inflammation of the tendon sheath), dactylitis or “sausage digit” (inflammation of entire digit), and enthesitis (insertion of the tendon).⁴

As with other sero-negative spondylarthropathies, there can also be extra-articular manifestations of PsA. These features may include inflammation of the eye, mucous
membranes, urinary system, and cardiovascular system (i.e., iritis, conjunctivitis, aortic dilation, and urethritis).⁶

There does not appear to be a difference in the prevalence of psoriasis between the sexes,⁷ however, the onset of disease seems to be earlier in women.⁸ The onset of psoriasis is bimodal with a median age of onset at 29.1 years.⁹ Those with early disease can have a greater body surface area involved, unstable psoriasis, frequent relapses, and a higher incidence of guttate psoriasis and nail involvement.^9,10

Patients with later onset tend to have a more stable course and less severe disease, but more frequent palmoplantar pustulosis.^9,10

The temporal sequence of disease onset can vary, making the diagnosis of PsA difficult. As high as 75%-80% of psoriasis patients will present with cutaneous manifestation 5-10 years prior to the onset of joint complaints.4,11 There can exist a flare in arthritis with or without a coinciding flare of psoriasis.4

The majority of patients with PsA have mild or moderate cutaneous manifestation,12 and 80%-90% of this population have nail lesions.^12,13 However, 46% of patients with psoriasis (no affected joints) have nail involvement.¹³ The extent and severity of both skin and joint disease correlate closely with the severity of psoriatic nail involvement, however this association is more commonly found in the DIP arthritis form of PsA.¹⁴

Differential Diagnosis

Distinguishing PsA from other inflammatory conditions can be challenging since the clinical features may overlap. The differential diagnosis may include: rheumatoid arthritis (RA), reactive arthritis, inflammatory bowel disease (IBD) and ankylosing spondylitis, to name a few. (See Table 2.)

To further complicate matters, other rheumatologic conditions such as osteoarthritis, soft tissue rheumatism, septic arthritis, and true RA can coexist with psoriasis. In addition, psoriasis has been found to occur with higher frequency in patients with IBD and ankylosing spondylitis.^15,16,17

The presence of such confounding variables stresses the importance of a full history and physical examination that includes serological, radiological, and perhaps genetic investigations to aid in the diagnosis.

Making the Diagnosis

There exist several PsA classification criteria in the literature. The Classification criteria for Psoriatic Arthritis (CASPAR) are newly developed criteria for the diagnosis of PsA. They are simple to use, have a high specificity of 98.7%, and a sensitivity of 91.4% for the diagnosis of PsA.18

CASPAR Criteria

A patient must have inflammatory articular disease (joint, spine, or entheseal) with 3 or more of the following 5 criteria:

1. Current OR personal history of psoriasis, OR family history of psoriasis (1st or 2nd degree relative). Psoriasis is defined as skin or scalp disease.
2. Psoriatic nail disease including: onycholysis, pitting, hyperkeratosis on current physical exam
3. Negative for rheumatoid factor (by any method except latex)
4. History of or current dactylitis recorded by a rheumatologist
5. Radiographic evidence of juxta-articular new bone formation, appearing as ill defined ossification near joint margins (but excluding osteophyte formation) on plain radiographs of the hand or foot.

Based on these criteria and established clinical features of PsA, a basic workup for a new patient in your office with psoriasis should include a history, physical examination, laboratory investigations, and review of treatment options as summarized below.

History

• Current OR personal history of psoriasis, OR family history of psoriasis
• Swelling of joints
• Pain or tenderness in joints
• Morning stiffness >30 minutes
• Functional capacity in activities of daily living (changes in ability to function at home and at work and impact on quality of life), etc.

Physical Examination

• Nails: evidence of onycholysis, pitting, hyperkeratosis, oil-drop sign, and nail crumbling
• Skin: see Table 1.

Musculoskeletal

• Signs of joint inflammation such as swelling, effusion, synovial thickening, erythema, decrease in range of movement
• Other manifestations: DIP joint involvement, enthesis, dactylitis, spondylitis and sacroiliitis, eye symptoms (i.e., iritis), etc.
• See Table 1 for other characteristic findings for PsA.

Diagnostic Investigations

• Laboratory tests should include: complete blood count, erythrocyte sedimentation rate, C-reactive protein, Rh factor, and routine renal and liver function tests.
• Plain radiographs: these can be normal in the early stages of disease. However, juxta-articular new bone formation, periarticular osteopenia, and later stages may demonstrate “pencil in cup” erosive disease in the hands or feet.

Treatment

When treating the cutaneous and joint manifestations, as in PsA, each aspect of the disease must be considered. The 2 may be treated independently, although a number of
systemic therapies may benefit both. Treatment options that can improve both PsA and psoriasis include:

1. Traditional systemic agents

• Cyclosporine (3-5mg/kg PO daily)
• Methotrexate (doses ranging from 15-25mg PO/IM weekly)

2. Biologic agents (with indication for PsA)

• Etanercept (50mg SC bi-weekly)
• Infliximab (5mg/kg IV at week 0, 2, 6 and then every8 weeks)
• Adalimumab (40mg SC every 2 weeks)

However, some may help one while adversely affecting the
other. Drugs that can induce disease exacerbation include:²⁰

1. Drugs that treat arthritis, but may worsen psoriasis

• Gold
• Systemic corticosteroids
• Hydroxychloroquine

2. Drugs that treat psoriasis, but may worsen arthritis

• Acitretin
• Efalizumab

The Role of the Dermatologist

The recognition and early treatment of PsA is analogous to that of acne. We are aware of the importance of early recognition of acne and the urgency in treating it aggressively in order to induce remission and prevent further damage. The destruction of the joints in PsA follows the same principle: treat early to prevent the damage. The dermatologist who monitors a psoriatic patient can detect PsA at its earliest stage.

A study by Zanolli and Wikle concluded that a large portion of patients with psoriasis presenting to a dermatologist for treatment were recognized to have coexisting joint complaints; and the prevalence of PsA is greater than that identified by a nondermatologist.²¹

The prevalence of psoriasis is greater than PsA, and psoriasis typically precedes the joint complaints.^4,11,22 Therefore, the dermatologist is in a unique position to screen patients with
psoriasis for PsA by maintaining a high index of suspicion and close follow-up. In limited cases, consultation with a rheumatologist may be necessary to make the diagnosis of PsA.

A screening questionnaire could be designed for patients presenting to the dermatologist for the first time with psoriasis. The Psoriasis and Arthritis Screening Questionnaire (PASQ)²³ that was developed by our group was created using the CASPAR criteria as its framework. This questionnaire does not replace a proper history, but reminds us to consider the diagnosis of PsA in any patient with symptoms of psoriasis, regardless of the severity of the cutaneous
manifestations.

Conclusion

The dermatologist is in a strategic position for early diagnosis, intervention, and appropriate management of the patient with PsA at its onset. The skin and joint involvement
in PsA can significantly affect a patient’s function and quality of life, and may increase cardiovascular morbidity and mortality.²⁴ These effects, in turn, may have significant impact on the family and society in general. Early diagnosis and effective therapy for PsA can prevent the progression of joint damage, and possibly induce a remission of the disease.

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