What are the diagnostic criteria for psoriasis?

From the Guidelines

Diagnosing psoriasis typically involves a thorough physical examination by a dermatologist or healthcare provider who will look for characteristic skin changes, such as well-defined, red, scaly patches or plaques with silvery-white scales, commonly found on the elbows, knees, scalp, and lower back, as described in the joint AAD-NPF guidelines of care for the management and treatment of psoriasis 1.

Key Diagnostic Steps

• A thorough physical examination by a dermatologist or healthcare provider to look for characteristic skin changes
• Examination of the skin, scalp, and nails while asking about medical history, including family history of psoriasis
• In some cases, a skin biopsy may be performed to confirm the diagnosis and rule out other skin conditions
• Blood tests may also be ordered to rule out other conditions or to determine the type of psoriasis
• Scoring systems like the Psoriasis Area and Severity Index (PASI) may be used to assess the extent and severity of the condition, as mentioned in the 2021 joint AAD-NPF guidelines of care for the management and treatment of psoriasis with topical therapy and alternative medicine modalities for psoriasis severity measures 1

Importance of Early Diagnosis

Early and accurate diagnosis is crucial as psoriasis is a chronic condition requiring long-term management, and delayed diagnosis can lead to increased morbidity and mortality, as well as a significant impact on quality of life, as highlighted in the 2019 joint AAD-NPF guidelines of care for the management and treatment of psoriasis with awareness and attention to comorbidities 1.

Diagnostic Considerations

• Psoriasis can be severe irrespective of the total body surface area (BSA) involved, when it has serious emotional consequences or occurs in select locations, including the hands, feet, scalp, face, genital area, or when it causes intractable pruritus, as noted in the 2021 joint AAD-NPF guidelines of care for the management and treatment of psoriasis with topical therapy and alternative medicine modalities for psoriasis severity measures 1
• The Psoriasis Area Severity Index (PASI) is a more specific means of quantifying the extent and severity of psoriasis, taking into account not only BSA but also the intensity of redness, scaling, and plaque thickness, ultimately producing a score from 0 (no disease) to 72 (maximal disease severity), as described in the 2019 joint AAD-NPF guidelines of care for the management and treatment of psoriasis with awareness and attention to comorbidities 1

From the Research

Diagnosing Psoriasis

To diagnose psoriasis, several methods and considerations are taken into account. The diagnosis is primarily based on characteristic physical findings and history 2.

Clinical Diagnostic Guidelines

Given the varied clinical presentations of psoriasis and its mimicry to other papulosquamous skin diseases, it may be challenging for non-dermatologists to diagnose psoriasis. Currently, no diagnostic criteria for plaque psoriasis have been validated in clinical studies 2.

Measures of Disease Severity

Several measures are used to assess the severity of psoriasis, including:

• Body Surface Area (BSA)
• Psoriasis Area and Severity Index (PASI)
• Psoriasis Log-based Area and Severity Index (PLASI)
• Self-Administered PASI (SAPASI) 3 These measures help in evaluating the effectiveness of treatments and the severity of the disease.

Histopathological Findings

Histopathological examination of skin biopsies can also aid in the diagnosis of psoriasis. A study found that conventional treatment modalities provided histopathologically significant recovery in psoriasis, but they did not have an effect on some histopathological findings 4.

Key Points for Diagnosis

• Characteristic physical findings and history are primary bases for diagnosis
• No validated diagnostic criteria for plaque psoriasis
• Several measures of disease severity are used, including BSA, PASI, PLASI, and SAPASI
• Histopathological examination can aid in diagnosis and assessing treatment response
• Further research is needed for long-term outcomes and safety profiles of treatments 5