Psoriasis is a cutaneous disorder which is commonly encountered in clinical practice.  It is characterized by rapid proliferation and abnormal differentiation of the epidermal keratinocytes.  The etiology is believed to be immunologic (strong association with activated T cells).  The initial occurrence may be at any age with a mean of approximately 30 years.  Men and women are equally affected with females being affected at a much younger age.  A positive family history is common.  Disease flares may occur in response to trauma, cold weather, infections, medications, smoking, and a compromised immune system.  Medications which may exacerbate symptoms include oral corticosteroids, lithium, antimalarial medications, interferon, ACE inhibitors, and beta blockers.  Lesions may affect any area of the skin.  Some patients manifest disease only as multiple pitting of their fingernails; whereas, others are stricken with lesions over a large percentage of their body.  While the diagnosis is often made on physical findings, some cases may require skin biopsy, KOH prep or serologic testing to rule out other conditions such as fungal infections, syphilis, eczema, pityriasis, rubra pilaris, drug reaction, seborrheic dermatitis, glucagonoma syndrome, and cutaneous T-cell lymphoma.  In persons with at risk behavior, the sudden onset of psoriasis may indicate underlying HIV infection.  There are several different types of psoriasis.

     Plaque psoriasis (psoriasis vulgaris) is the most common form of disease.  Lesions have a propensity for the elbows, knees, scalp, umbilicus, lumbosacral region, genitalia, and gluteal cleft, and are characterized by erythematous plaques with an overlying silver scale.  Removal of the overlying scale with manual abrasion reveals underlying areas of pinpoint hemorrhage, a phenomenon known as the Auspitz sign.  Woronoff’s ring refers to the area of pallor surrounding each lesion.  Resolution of lesions occurs from the center outward producing an annular appearance initially.  Geographic tongue may be an associated finding.  The Koebner phenomenon occurs when new plaques develop in response to trauma such as burns, friction, sunburn, contact dermatitis, chemical irritation or tattooing.

     Guttate psoriasis is an acute form of psoriasis with lesions that are smaller (0.1 to 1.0 cm in diameter) and thinner than those of plaque psoriasis.  Children and young adults are often affected.  Lesions may develop on the trunk, proximal areas of the extremities, or face.  Patients with underlying plaque psoriasis may develop acute flares of guttate psoriasis.  Some cases occur following upper respiratory tract infections with goups A,C, or G streptococci.

     Pustular psoriasis is characterized by the development of sterile pustules.  Factors which are associated with disease flares include cigarette smoking, oral contraceptives, pregnancy and corticosteroids.  Pustular sporiasis may be of two types.  Localized pustular psoriasis involves the palms and soles (palmoplantar pustulosis).  Affected patients are generally over 50 years of age.  This is a refractory form of disease.  The most effective form of treatment appears to be the retinoid acitretin (30-50 mg PO QD) either as a single agent or in conjunction with psoralen-ultraviolet A therapy.  Smoking cessation should be strongly encouraged.  Acrodermatitis continua (Hallopeau’s acrodermatitis) refers to a form of localized pustular posriasis that is localized to the distal fingers and toes.  Hallopeau’s acrodermatitis is often refractory to treatment.  Generalized pustular psoriasis (von Zumbusch’s psoriasis) represents a potentially life threatening emergency.  It is characterized by the development of multiple pustules over erythematous lesions with associated systemic symptoms to include fever, mailaise, arthralgias, and diarrhea.  It may be the sole occurrence or may manifest in patients with underlying plaque psoriasis.  The pustules progress into lakes of pus.  The lesions then desquamate and move to new areas.  Associated laboratory abnormalities include leukocytosis, hypocalcemia, and hypoalbuminemia.  Acutely, patients should be hospitalized for aggressive supportive therapy until stabilized.

     Erythrodermic psoriasis refers to a pruritic, red inflammatory cutaneous process that affects most or all of the body.  Associated systemic symptoms may include fever, chills, pruritus, malaise, fatigue, lower extremity edema, and hypothermia.  Mortality results from high-output heart failure, pneumonia or renal failure.  This often occurs as a flare in patients with chronic plaque psoriasis affecting up to 2% of patients with underlying psoriasis.  Flares of erythrodermic psoriasis are precipitated by systemic illnesses, stress, alcoholism, and the improper use of corticosteroids (oral, topical, and intramuscular).  Therapy may require hospitalization until the patient is stable enough to undergo aggressive treatment for their psoriasis.  After suffering a flare of erythrodermic psoriasis, most patients revert to their prior level of psoriatic involvement.  Flares of erythrodermic disease are usually not recurrant.

     Psoriatic involvement may be limited to the genitalia in male patients.  The two forms of genital psoriasis include inverse psoriasis and penile psoriasis.  Inverse psoriasis may present as red, well-defined inguinal plaques that may affect the scrotum, inguinal folds and penis.  Inverse psoriasis may be associated with pruritis.  Penile psoriasis may respond to low dose topical steroids (hydrocortisone 2.5%), combination therapy with low dose topical steroid cream plus ketoconazole cream, or Dovonex cream.

     Psoriatic arthritis is an associated condition in which patients suffer from a progressive, seronegative spondyloarthropathy.  Multiple joints are affected including the knees, ankles, metatarsophalangeal joints and the proximal interphalangeal joints.  Different patterns of joint involvement include predominantly distal interphalangeal arthritis (classic pattern), arthritis mutilans (osteolysis of phalanges, metacarpals, and metatarsals with resultant “opera glass” digits with redundant skin), symmetric polyarthritis (joint involvement resembles rheumatoid arthritis except there are no systemic symptoms and rheumatoid factor is absent), oligoarthritis (most common form of psoriatic arthritis), spondylitis and sacroiliitis.  Radiographic abnormalities may include ankylosis, sacroiliitis, joint space narrowing and syndesmophytes.  Nonspecific lab abnormalities include an elevated ESR, leukocytosis, and an association with the HLA-B27 antigen.  A physical finding which is characteristic of psoriatic arthritis (although it is also encountered in Reiter’s syndrome) is dactylitis or the sausage digit.  Sausage digit refers to a diffusely swollen digit which occurs secondary to inflammation of the underlying tendons and periosteum.  Enthesopathy (tendon inflammation at the point of its junction with bone) is also noted and often occurs at the insertion of the Achilles tendon into the calcaneus.  Patients usually develop symptoms of psoriatic skin involvement first, but some may have no signs of disease or more commonly, disease is localized in discrete locations (anal crease, scalp, genitalia, umbilicus, or nails).  In some patients, the symptoms of arthritis precede cutaneous manifestations of psoriasis.

     Therapy for psoriasis is varied depending on the type of disease.  For plaque psoriasis, initially topical therapies are employed to include steroids, emollients, calcipotriene, tazarotene, anthralin, keratolytics (salicylic acid, lactic acid and urea) and coal tar products.  If emollients and keratolytics fail to control symptoms, then more aggressive therapy is required.  Intermediate to high potency steroid agents are used initially for the first few weeks or until an effect is noted and then the potency is decreased and eventually discontinued as tolerated.  Gels are a more effective medium than creams.  Application of an overlying occlusive dressing increases topical medication absorption.  Since steroids are not without adverse consequences, a steroid sparring agent (calcipotriene, tazarotene, coal tar, or anthralin) should be added at the initiation of therapy and continued to maintain control after the topical steroid has been discontinued.  Effective topical combination therapies include: clobetasol ointment and 10% salicylic acid, halobetasol and calcipotriene, and sequential applications of corticosteroid ointments and tazarotene.  Combinations which should be avoided include: salicylic acid and calcipotriene and calcipotriene in conjunction with hydrocortisone valerate.  If topical therapies or combinations of topical therapies prove ineffective, referral to a dermatologist should be considered for phototherapy, systemic therapy (retinoids, methotrexate, cyclosporin, sulfasalazine, hydroxyurea, azathiprine, etc) or a combination of phototherapy and other treatments (PUVA).  Acitretin is effective for pustular and erythrodermic psoriasis.  All women of childbearing age need to be on birth control when receiving acitretin therapy.  Methotrexate is effective in the treatment of plaque, erythrodermic, and pustular psoriasis. Other potential therapies include cyclosporine, mycophenolate mofetil, oral tacrolimus, hydroxyurea in combination with retinoids or phototherapy, and thioguanine.  Therapy for psoriatic arthritis may include NSAIDs (meclofenamate may be preferable), methotrexate, or gold salts in conjunction with a physical therapy program centered at maintaining strength and mobility.