Approach Considerations

The diagnosis of psoriasis is clinical. The differentiation of psoriatic arthritis from rheumatoid arthritis and gout can be facilitated by the absence of the typical laboratory findings of those conditions. Overlap with other arthritic syndromes is possible, however.

Laboratory Studies

Laboratory studies and findings for patients with psoriasis may include the following:

Test result for rheumatoid factor (RF) is negative.
Erythrocyte sedimentation rate (ESR) is usually normal (except in pustular and erythrodermic psoriasis).
Uric acid level may be elevated in psoriasis (especially in pustular psoriasis), causing confusion with gout in psoriatic arthritis.
Fluid from pustules is sterile with neutrophilic infiltrate.
Perform fungal studies. (This is especially important in cases of hand and foot psoriasis that seem to be worsening with the use of topical steroids.)

If starting systemic therapies such as immunological inhibitors, consider obtaining baseline laboratory studies (ie, complete blood cell [CBC] count, blood urea nitrogen [BUN]/creatinine, liver function tests [LFTs], hepatitis panel, tuberculosis [TB] screening, and pregnancy test).

Other Tests

Although most cases of psoriasis are diagnosed clinically, some, particularly the pustular forms, can be difficult to recognize. In these cases, dermatologic biopsy can be used to make diagnosis. Biopsy of the skin lesion may reveal basal cell hyperplasia, proliferation of subepidermal vasculature, absence of normal cell maturation, and keratinization. A large number of activated T cells are present in the epidermis. Biopsy of acral skin may be less useful as chronic eczematous dermatitis may be psoriasiform and psoriasis of the palms and soles may show spongiosis more often associated with eczema.

Radiographs of affected joints can be helpful in differentiating types of arthritis. Joint x-rays can facilitate the diagnosis of psoriatic arthritis. Bone scans can identify joint involvement early.

Conjunctival impression cytology has demonstrated an increased incidence of squamous metaplasia, neutrophil clumping, and snakelike chromatin.

When the scales are removed, small droplets of blood appear within a few seconds from exposed vessels in the dermal papillae; this is known as the Auspitz sign.

Procedures

Punch biopsy of the skin may act as a confirmatory workup procedure.

Histologic Findings

Histopathology findings include the following^[38]:

Regular acanthosis of the epidermis
Parakeratosis
Kogoj spongiotic pustules
Munro microabscesses

Treatment & Management

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Media Gallery

Plaque psoriasis is raised, roughened, and covered with white or silver scale with underlying erythema. Contributed by Randy Park, MD.
Guttate psoriasis erupted in this patient after topical steroid therapy was withdrawn during a pregnancy. Contributed by Randy Park, MD.
Plaque psoriasis is most common on the extensor surfaces of the knees and elbows. Contributed by Randy Park, MD.
Nail psoriasis. Pits, distal onycholysis (nail separation), and brownish staining ("oil spots") are classic nail findings
Inverse psoriasis. Occurring in skin folds, this will often lack the scale seen in other locations.
Pustular psoriasis of the soles. This may be confined to the hands and feet (Acrodermatitis Continua of Hallepeau) or may be part of a generalized pustular psoriasis (Von Zumbusch disease)

of 6

Author

Jacquiline Habashy, DO, MSc Resident Physician, Department of Dermatology, Western University of Health Sciences College of Osteopathic Medicine of the Pacific

Jacquiline Habashy, DO, MSc is a member of the following medical societies: American Osteopathic College of Dermatology

Disclosure: Nothing to disclose.

Coauthor(s)

David T Robles, MD, PhD, FAAD Dermatologist, Oak Tree Dermatology

David T Robles, MD, PhD, FAAD is a member of the following medical societies: American Academy of Dermatology

Disclosure: Nothing to disclose.

Chief Editor

William D James, MD Paul R Gross Professor of Dermatology, Vice-Chairman, Residency Program Director, Department of Dermatology, University of Pennsylvania School of Medicine

William D James, MD is a member of the following medical societies: American Academy of Dermatology, Society for Investigative Dermatology

Disclosure: Received income in an amount equal to or greater than $250 from: Elsevier; WebMD<br/>Served as a speaker for various universities, dermatology societies, and dermatology departments.

Additional Contributors

Jeffrey Meffert, MD † Former Associate Clinical Professor of Dermatology, University of Texas School of Medicine at San Antonio

Jeffrey Meffert, MD is a member of the following medical societies: American Academy of Dermatology, American Medical Association, Association of Military Dermatologists, Texas Dermatological Society

Disclosure: Nothing to disclose.

Acknowledgements

Robert Arffa, MD Clinical Assistant Professor, University of Pittsburgh School of Medicine

Robert Arffa, MD is a member of the following medical societies: American Academy of Ophthalmology