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Image : “psoriasis” by
Hans. License: CC0



Psoriasis plaque . In higher resolution the silvery whitish remnants of the fallen skin layer are visible

Image: Plaque psoriasis. In higher resolution, silvery-white scales of exfoliated skin can be seen. By Eisfelder, License: CC BY-SA 3.0

Psoriasis (psoriasis vulgaris) is a chronic, relapsing skin disorder characterized by inflammation and hyperproliferation of skin cells. Patients present with patches of skin covered with silvery scales, which is why this disease is also referred to as plaque psoriasis. It is caused by a number of environmental, genetic, and immunological factors.


Although psoriasis occurs in individuals worldwide, it mostly affects fair-skinned people. The prevalence in Europe and North America is about 2–3%. In Africa and Asia, psoriasis is rare. For indigenous people, the disease is practically irrelevant.


The cause of psoriasis has not been determined; however, there is a clear genetic predisposition. The disease probability for a child whose parents both have psoriasis is about 50%. In identical twins, the probability rises to 66%.

Psoriasis is also associated with various HLA antigens. A connection with other immunological factors, such as T lymphocyte activity, is considered likely. Since endogenous antigens stimulate specific groups of T cells, which ultimately leads to an increased division rate of the keratinocytes through a more complex pathomechanism, psoriasis is also associated with autoimmune diseases.

Based on these defective immunological and autoimmune responses, a huge increase in certain metabolic processes and cell division rates occurs. An average of 0.4% of the cells of the basal cell layer continuously undergo cell division in healthy skin. Psoriatic skin has a cell division rate of 2.5%.

The time of cell division also substantially increases in psoriatic skin. Cells in healthy skin typically need 20 days to divide. Psoriatic skin cells take about 1.5 days to divide. The transit time of the cell from the basal cell layer to the secretion of lamellar bodies in the horny layer is significantly lower. Cells of psoriatic skin pass through the individual skin layers within 3–4 days compared to 28 days for healthy skin.

Risk factors for psoriasis include streptococcal infections, which may raise the severity of psoriasis; staphylococcal infection; medications such as beta-blockers, interferon, and lithium; stress, alcohol use, and strong mechanical stimuli (Koebner phenomenon).


Psoriasis typically manifests acanthosis, hyperkeratosis, and parakeratosis. The epidermis is enlarged and the epidermal endplates are thinned. In the dermis, lymphocytic infiltration can be found. The cells of the prickle cell layer (stratum spinosum) are markedly enlarged due to the general increase in metabolic processes. At the same time, the accelerated processes result in an incomplete differentiation of the individual squamous epithelial layers of the epidermis, causing thick, silvery scaling.

Clinical presentation

Main symptoms

The clinical picture of psoriasis is highly variable. The most common sites for skin lesions are the elbows, scalp, knees, lumbosacral region, natal cleft, and glans penis. The individual psoriatic foci usually do not itch; however, predilection sites such as the head and anal region do tend to itch.

The typical lesion presents as sharply defined, usually roundish, erythematous plaques with silvery scaling. Typical predilection sites are the extensor surfaces of the elbows and knees, the hairy areas of the head, the navel, and the sacral region.

However, psoriatic lesions can appear on any part of the integumentary system. The size of the lesions varies widely, ranging from dot-like inflammations to confluent, plate-sized, scaly surfaces.

The following 3 phenomena are present in each psoriatic lesion:

1. Candle phenomenon

The thick, silver-gray scales scraped off of inflamed skin resemble the scrapings of candle wax.

2. The phenomenon of the last epidermal layer

Below the thick scales, a cohesive, sheet-like membrane can be found, which corresponds to the deepest layer of the epidermis.

3. Auspitz’s sign (blood dew)

If the last layer is removed, punctate bleeding spots are revealed.

Pitting his fingernails in psoriasis

Image: Pitting of fingernails in psoriasis. By Goodbye, License: CC BY-SA 3.0

Other symptoms

Nails: Nail changes are seen in 30–50% of all psoriasis cases. Typical signs include dotted or pitted nails, crumbling  nails, a yellowish discoloration of the nail bed (oil drop), and distal onycholysis.

Mucous membranes: Mucous membranes are affected less frequently than the nails. The changes take the form of leukoplakia.

Joints: In some cases (about 5–8%), immunological involvement of the joints occurs. Psoriatic arthritis (or psoriasis arthropathica) is a chronic inflammatory condition. The central lesion in the joint, called synovitis, causes cartilage destruction and bone erosion. Psoriatic arthritis frequently affects large joints, but as the inflammatory process continues, deviation of the fingers may occur.

Magnetic resonance images of the fingers in psoriatic arthritis

Image: Magnetic resonance images of the fingers in psoriatic arthritis. Shown are T1-weighted (a) pre-contrast and (b) post-contrast coronal images. Enhancement of the synovial membrane at the third and fourth proximal interphalangeal (PIP) and distal interphalangeal (DIP) joints are seen, indicating active synovitis (inflammation of the synovial membrane; large arrows). There is joint space narrowing with bone proliferation at the 3rd PIP joint, and erosions are present at the 4th DIP joint (white circle). Extracapsular enhancement (small arrows) is seen medial to the 3rd and 4th PIP joints, indicating probable enthesitis (inflammation of a tendon insertion). By Fiona McQueen, Marissa Lassere, and Mikkel Østergaard, License: CC BY 2.0

Pustular psoriasis

Skin irritations are often caused by an infection or as a response to a drug. While this may not cause any further problems in an otherwise healthy person, it can result in the massive formation of pustules in a psoriasis patient. These pustules are primarily filled with neutrophilic granulocytes. The generalized form (generalized pustular psoriasis) leads to a greatly accelerated erythrocyte sedimentation rate (ESR) and leukocytosis with a left shift.

Diagnosis and differential diagnosis

There are no specific lab investigations for psoriasis. In the majority of cases, the clinical picture is enough for an accurate diagnosis, though uncertain cases may require a biopsy. The histological picture corroborates the suspicion.

Differential diagnosis includes the following:

  • Blood tests for rheumatoid factor
  • ESR: It is normal in psoriasis cases, but elevated in the pustular type
  • Uric acid
  • Fungal studies
  • Dermatological biopsy
  • Radiological studies of joints

These investigations are conducted to rule out the following:

  1. Scaly fungal infection or seborrheic dermatitis
  2. Acute exacerbation of neurodermatitis, which may be confused with psoriasis
  3. Because psoriasis can affect the joints in some cases, the differential diagnosis must take into account rheumatic diseases.


The established treatment approaches are purely symptomatic. Psoriasis is a protracted disorder that is difficult to treat except for rare cases of spontaneous healing.

Local therapy

  • Dithranol: The most important drug for topical treatment is dithranol (anthralin). With proper dosage and correct exposure time, it results in a long-lasting remission of the lesions.
  • Vitamin D3: Vitamin D analogs such as calcipotriol or tacalcitol are very effective in the treatment of psoriatic hyperproliferation.
  • Phototherapy: Ultraviolet light therapy is used in combination with oral medications that make the skin more photosensitive (psoralen plus ultraviolet A, also known as PUVA therapy). Alternatively, a combination of UV light while irritating the skin with salt water can be considered (PUVA bath therapy).
  • Corticosteroids: Treatments with corticosteroids should be short-term and only carried out in special cases. Risks with treatment include rebound phenomenon, atrophy, and the proliferation of vessels. Corticosteroids are helpful when treating unfavorably located spots such as the head and anal area.

Systemic therapy

  • Acitretin is a retinoid usually used for pustular forms of psoriasis. This medication is not recommended for women of childbearing age and patients with liver damage.
  • Fumaric acid ester is given in extensive cases of psoriasis vulgaris. Therapy should start with low dosages and increase slowly. Side effects occur mostly include gastrointestinal symptoms such as nausea, vomiting, and diarrhea. The medication has a significant immunosuppressive effect due to lymphocyte depression caused by the medication.
  • Cyclosporine is used for all forms of psoriasis. Kidney function and blood pressure should be checked regularly (drug monitoring) because this therapy may diminish renal function.


Psoriasis is an immunological reaction (autoimmune disease). Trigger factors include streptococcal infections, medications, stress, alcohol, and mechanical stimuli.

Scaly, inflammatory psoriatic lesions are caused by an increased rate of mitosis of the basal layer (stratum basale), an accelerated cell division time, and reduced cell transit time.

Typical of psoriatic lesions:

  • Candle phenomenon
  • The phenomenon of the last epidermal layer
  • Auspitz’s sign

The major forms of psoriasis are:

  • Plaque psoriasis
  • Psoriatic arthritis
  • Pustular psoriasis

Treatments include both local and systemic options.

Psoriasis has 2 peak ages: from age 16–20 and from age 57–60.


Psoriasis has a tendency for remission with phases of improvement. Symptoms flare up mainly because of stress and other infections.

Dermatoses of the Pityriasis Group

Pityriasis refers to flaking or scaling of the skin. The dermatoses of the pityriasis group include pityriasis rosea, pityriasis lichenoides chronica, and pityriasis rubra pilaris.

Pityriasis rosea

Definition and epidemiology

Pityriasis rosea is an acute inflammatory skin disease with a time-limited progression. The usual onset age is between 10 and 40 years old. It occurs most frequently in the autumn and winter months.


Although the cause is not fully understood, it is now believed that the disease probably has infectious origins. The pathogen has not yet been definitively identified, but it could be a virus.

Pityriasis rosea may be associated with allergies, mainly the allergy type IV (delayed-type).


Edema in the upper dermis is typically present. Infiltrations of lymphocytes and a moderately widened epidermis are also apparent. The visibly noticeable scaling of the skin is histologically reflected in a para- or hyperkeratosis.

Clinical presentation

Pityriasis rosea typically starts with a single, sharply defined, oval plaque which is also referred to as primary plaque, primary medallion, or herald patch.

The patch is pale red with desquamation and scales at the margins. It is usually found on the torso.

Secondary outbreaks develop within 2 weeks. They exhibit the same clinical picture as the primary efflorescence lesions. However, these lesions are smaller, making it possible for the clinician to diagnose them even weeks later. Secondary outbreaks tend to occur symmetrically on the torso and proximal extremities and usually extend into the main lines of the body. Head, neck, and distal extremities are not affected in the majority of cases.

Flu-like symptoms may precede the skin manifestation. The patient rarely complains of itching. Cervically, it can sometimes lead to moderate lymphadenopathy.

Pityriasis rosea usually dissipates after 4–6 weeks.

Diagnosis and differential diagnosis

The primary outbreak, as well as the exanthematous distribution of secondary outbreaks (main voltage lines), are indicative of pityriasis rosea. Superficial tinea corporis, secondary syphilis, and an exanthematous psoriasis guttata should be considered as differential diagnoses.


Since the lesions regress on their own after at least 6 weeks, there is no need for treatment of pityriasis rosea. Itching is rarely observed and can be treated with antihistamines such as cetirizine or Fenistil if needed. Rehydrating therapy should be avoided, as this worsens the disease.

Pityriasis lichenoides chronica

Definition, etiology, and epidemiology

Pityriasis lichenoides chronica is a subacute inflammatory dermatosis characterized by papular or squamous lesions. It occurs worldwide and is most frequently seen in adolescents and adults under age 30. The etiology is unknown. Immune response due to infection and allergy is suspected.

Clinical presentation

Brownish-red papules and plaques that can reach the size of a penny, with flakes that can be lifted off with a spatula, are typical for pityriasis lichenoides chronica. It is accompanied by minor itching. Complete healing occurs within weeks or months.


The diagnosis is based on the identification of the reddish-brown lesions combined with the corresponding scaling. Other symptoms are generally absent. Psoriasis, papulosis, and syphilis should be considered as differential diagnoses.


Pityriasis lichenoides chronica usually resolves on its own. As an accompanying measure—or when complications arise—carefully dosed ultraviolet B phototherapy and corticosteroids may be used.

Pityriasis rubra pilaris

Definition, etiology, and epidemiology

Pityriasis Rubra Pilaris (PRP) is a type of papulosquamous skin condition. Typical peak age does not exist. Men and women are equally affected. The etiology is unknown. Two forms occur in adults: classic and atypical PRP.

Clinical presentation

The classic adult form (type I) is characterized by follicular, erythematous, and hyperkeratotic papules. It commonly affects the torso and extensor surfaces of the extremities. It is associated with extensive erythema with flaking, which can escalate up to erythroderma. In its course, PRP typically exhibits a craniocaudal direction of development. Other symptoms include palmoplantar keratosis and thickened nails with distal splinter hemorrhages.


In 80% of the cases, a spontaneous remission within 1–3 years is observed. Vitamin D3 analogs and retinoids are medications of choice.

Reactive arthritis (formerly known as Reiter’s syndrome)

Definition and epidemiology

Reiter’s dermatosis is one of the main symptoms of Reiter’s disease. The disease is characterized by the clinical triad urethritis, conjunctivitis, and arthritis. If dermatosis is also observed, this is called Reiter’s tetrad.

Balanitis circinata, psoriasis-like lesions, and keratoderma blennorrhagicum on the palms and soles characterize the cutaneous symptoms of this inflammatory, chronically relapsing disease.


Genetic predisposition (HLA-B27) is suspected. At the same time, the disease is assumed to have infectious and allergic origins.

Clinical presentation and diagnosis

histopathology in an acute case of gonococcal urethritis using gram stain technique

Image: Histopathology in an acute case of gonococcal urethritis using gram stain technique. By CDC/ Joe Millar, License: Public domain

Common symptoms of Reiter’s disease include:

  • Urethritis (urogenital inflammation)
  • Conjunctivitis (iritis)
  • Arthritis (oligoarthritis)
  • Reiter’s dermatosis (balanitis, keratoderma)

Possible accompanying symptoms include:

  • Fever
  • Systemic inflammatory signs
  • Iliosacral arthritis
  • Internal organ involvement (carditis, pleurisy, etc.)

Symptoms of the skin

Dermatosis can be found in about 10% of the cases of patients with Reiter’s disease. The lesions are exudative. Since the exanthema may be pustular and confluent on the palms and soles of the feet, the so-called keratoderma blennorrhagicum develops. Since the hairy scalp and the nails may be affected as well, the lesions resemble those of psoriasis. Balanitis is found as both inflammatory and erosive efflorescence on the glans penis.


If a diagnosis cannot be confirmed with the symptom triad, various laboratory tests can be used as further indications:

  • No rheumatoid factors; no antistreptolysin titer
  • Bacteriological or serological indication of past infections; for example, of the bowel or the urogenital tract
  • Immunogenetically, frequently associated with HLA-B27


Truly effective treatment of Reiter’s disease does not exist. Locally, corticosteroids or vitamin D3 analogs can be used, if possible, in combination with PUVA or PUVA bath therapy. Methotrexate has been proven to be effective. For severe pustular lesions, acitretin can be applied. Urethritis is treated with tetracyclines.

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