Diagnosis: Psoriasis or not? What are the clues

Diagnosis: Psoriasis or Not? What are the Clues? Emily M. Altman and Hideko Kamino

Psoriasis is a common Inflammatory, hyperproliferative skin dlsorder that affects 1% to 2% of the population of Western Europe and the United States. Because the clinical presentation of psoriasis is varied, many times the definitive diagnosis depends on the histological examination. How- ever, the hlstological changes of psorlasis are as varied as the cllnlcal presentatlons. Therefore, a combination of histopathologic features must be present for the diagnosis of psoriasis to be made. In this adlcle, we revlew the clues for the hlstopathologlc dlagnosls of each type and stage of psorlasls, such as psoriasis vulgaris, pustular psoriasis, and erythrodermlc psoriasis, as well as the hlstopathologlc differential diagnosis of these entitles. Copyright �9 1999 by W.B. Saunders Company

p SORIASIS IS AN inflammatory, hyperproliferative skin disorder that affects 1% to 2% of the popula-

tion of Western Europe and the United States, but is infrequent in Africa and Asia and rare among the native North and South American populations. ~ Both genetic and environmental factors are thought to play a role in the initiation and progression of the disease. A family history for psoriasis is indicated by one third of the patients. Family studies, twin studies, and pedigree analyses point to a polygenic and multifactorial inheri- tance of psoriasis. 2 Among the documented environmental factors that affect the development and course of psoriasis are trauma and infection. 3 Other factors that may play a role in psoriasis are drugs, sunlight, stress, and HIV infection. Environmental factors such as streptococcal infection, stress, and colder climate are also associated with disease onset and/or severity. Earlier age of onset is thought to correlate with worse prognosis. 4 The strong association between psoriasis and certain human leukocyte antigen (HLA) types, namely HLA-B13, B175, and Cw66, the exocytosis of mononuclear cells prior to epidermal hyperplasia, and the efficacy of T cell-selective immunosuppressive treatments, such as cyclosporine, 7 FK506 s, and anti- CD4+ monoclonal antibody 9 in treating psoriasis, establish psoriasis as an immunologically-mediated dermatosis. The clinical course and prognosis of psoriasis is unpredictable, characterized by exacerbations and remissions. There is a variety of clinical types of psoriasis ranging from mild, localized plaques to generalized pustular psoriasis or erythroderma.

PSORIASIS VULGARIS: CLINICAL FEATURES

In nonpustular psoriasis, lesions may erupt as acute guttate papules or appear as chronic plaques. Initial lesions of guttate or eruptive psoriasis appear as pinpoint erythematous papules with central scaling that enlarge rapidly. Numerous small (0.5 to 1.5 cm) lesions appear simultaneously over the upper trunk and proximal extremities, sparing the scalp and intertriginous zones. Acute guttate psoriasis typically is characterized by an early age of onset and has a strong association with antecedent streptococcal throat infection. 1~

Psoriasis vulgaris (chronic plaque psoriasis) is the most frequent clinical form of psoriasis, ll In this form of psoriasis, the lesions develop slowly from erythematous macules to asymptomatic papules with a tendency to eventually become confluent, forming stable, elevated, sharply demarcated, erythematous plaques with a silvery, adherent (micaceous) scale. The sites of predilection include the scalp, elbows, knees, lower back, and umbilicus. The Auspitz sign is present in this type of psoriatic plaques. Psoriasis vulgaris may also involve the intertriginous zones (psoriasis inversa). The nails are frequently involved, with pitting, oil spots, and/or onychodystrophy. The lesions of chronic plaque psoriasis may remain stable for years, may occasionally involute, or may develop into erythrodermic or pustular psoriasis. During severe flares, psoriatic plaques may become studded with pustules.

PUSTULAR PSORIASIS: CLINICAL FEATURES

Pustular and erythrodermic psoriasis are less stable, more severe for the patient and more difficult to treat than guttate and plaque psoriasis. Pustular psoriasis is subdivided into two categories: generalized and local. Generalized pustular psoriasis is usually seen in middle- aged persons. 12 Males and females are affected equally. There is abrupt onset of widespread fiery erythema that may eventuate in erythroderma, sheets of pustulation, and scarlatiniform desquamation, accompanied by fe-

From the Dermatopathology Section, Department of Dermatol- ogy, New York University Medical Center, New York, NY

E.M.A. supported by the Holtzman Fellowship. Address reprint requests to Emily M. Altman, MD, New York

University Medical Center, 530 First Ave, Suite 7J, New York, NY 10016.

Copyright �9 1999 by W.B. Saunders Company 1085-5629/99/1801-0007510.00/0

Seminars In Cutaneous Medicine and Surgery, Vol 18, No I (March), 1999: pp 25-35 25

26 ALTMAN AND KAMINO

ver, malaise, leukocytosis, and an elevated erythrocyte sedimentation rate. Sterile pustules, 2 to 3 mm in diameter are disseminated over the trunk and the extremities, including the nail beds, palms, and soles, as well as in the oral and genital mucosa. Pustules may be asymptomatic or associated with burning and may coalesce to form lakes of pus 1 to 2 cm in diameter. The disease characteristically occurs in waves of fever and pustules. Typical extensive psoriasis usually precedes the acute pnstular flare for several years. The factors implicated in the development of pustular psoriasis include excessive topical medications, infections, stress, and the discontinuation of systemic corticosteroids. Impetigo herpetiformis most likely represents generalized pustular psoriasis precipitated by pregnancy, al- though some authors classify it as a separate and distinct disorder. 13 It is a superficial sterile pustular eruption on an erythematons base, accompanied by fever, toxicity, hypocalcemia, and sometimes tetany. 14 The eruption begins in flexural areas, as pustules at the periphery of erythematons patches, then becomes generalized. Impetigo herpetiformis usually remits after childbirth and is likely to recur in subsequent pregnan- cies. Pustules may also arise in previously existing psoriatic plaques during exacerbations of the disease. In palmar/plantar pustular psoriasis, sterile pustules develop in erythematous scaling plaques localized to the palms and soles. This form of psoriasis is characteristically indolent and resistant to treatment. In acrodermatitis continua, there is a chronic, localized area of scaling and sterile pustules that begins acrally on a finger or toe and remains localized to one or more digits for months or years. Systemic signs and symptoms are absent in localized forms of pustular psoriasis.

ERYTHRODERMIC PSORIASIS: CLINICAL FEATURES

Erythrodermic psoriasis (exfoliative erythroderma) is an acute condition that usually results from a progressive worsening of psoriasis in an acute or chronic fashion and affects 75% or greater of body surface area, including the face, trunk, and extremi- tiesJ 5 It frequently arises in patients with unstable psoriasis vulgaris. Erythrodermic psoriasis is clinically difficult to differentiate from erythroderma of other etiologies, such as pityriasis rubra pilaris, Sezary syndrome, severe atopic or allergic contact dermatitis, or drug eruption. The skin becomes diffusely and in- tensely red, warm, edematous and profoundly scaling to the point of generalized desquamation. There is usually associated pruritus. Constitutional symptoms, such as fever, chills, shortness of breath, and myalgias, are often present. Patients may have leukocytosis, electro- lyte imbalances, high output cardiac failure, abnormal liver function tests and Staphylococcus aureus bacteremia. The

etiological agents of erythroderma in psoriasis have been ascribed to intercurrent infections, harsh topical treatments, and withdrawal of systemic steroids.

CLUES TO THE HISTOPATHOLOGIC DIAGNOSIS OF PSORIASIS

Clinical diagnosis of fully developed plaque psoriasis rarely presents a problem. However, because the clinical presentation of psoriasis is so varied, often the definitive diagnosis depends on the histological examination. Histological changes of psoriasis are as varied in different types and at different stages of psoriasis as are the clinical presentations. Recognition of the various histological presentations of psoriasis is important in assisting the clinician in the diagnosis and treatment of this common skin disorder. Certain clues are present in the histopathologic specimens of psoriasis that in combination make the differentiation of psoriasis from other psoriasiform disorders possible.

Clues to the Diagnosis of Psoriasis (1) Dilated and tortuous capillaries in the papillary

dermis, that spiral to near the undersurface of the epidermis. These capillaries are frequently congested with erythrocytes, which may arrange themselves in stacks (the rouleau formation). Dilated papillary dermal vessels are present in all types and stages of psoriasis, and are still present in clinically resolved plaques of psoriasis after treatment.

(2) Papillary dermal edema. (3) Superficial perivascular, predominantly lympho-

cytic infiltrate. Neutrophils appear in the dermal papillary infiltrate as the lesion of psoriasis matures.

(4) Epidermal hyperplasia with elongated, thin, club-shaped rete ridges of even lengths (psoriasiform hyperplasia). In early psoriasis, the epidermal hyperplasia is slight or absent, and the rete ridges are of uneven lengths. The typical psoriasiform hyperplasia is present in mature plaques of psoriasis.

(5) Increased number of mitotic figures in basal and suprabasal locations.

(6) Markedly thinned suprapapillary plates. (7) Pallor of keratinocytes in the upper portions of

the epidermis. (8) Hypogranulosis: the hypogranulosis is focal in

early lesions of psoriasis, then becomes confluent with eventual disappearance of the granular layer in mature plaques.

(9) Parakeratosis with neutrophils: in early and guttate/eruptive lesions of psoriasis, the parakeratosis is disposed in distinct mounds, which are staggered within an orthokeratotic cornified layer. Neutrophils accumulate at the summits of these mounds. In mature lesions, neutrophils are arranged in tiers within the confluent parakeratotic cornified layer. Munro microab-

DIAGNOSIS: PSORIASIS OR NOT? 27

scesses are collections of neutrophils within the parakeratotic cornified layer. The spongiform pustule of Kogoj is a collection of neutrophils in the upper spinous layer immediately beneath the parakeratotic scale. At the periphery of the spongiform pustule, neutrophils are present between compressed keratinocytes. In pustular psoriasis, the accumulation of neutrophils in a subcorneal location is so massive that it gives rise to macropustules. Of all histological features of psoriasis, only the spongiform pustule of Kogoj and the Munro microabscess are considered diagnostic but not pathognomonic of psoriasis, and the histological diagnosis of psoriasis cannot be made with certainty in their absence. 16 However, spongiform pustules and neutrophils in mounds of parakeratosis may be seen in dermatophytosis and candidiasis.

In different types and at different stages of psoriasis, the above histological manifestations are present in varying degrees, and often it is the combination of these manifestations that helps the pathologist arrive at the diagnosis of psoriasis.

PSORIASIS VULGARI$: HISTOPATHOLOGIC FEATURES

HJstopathologJc Features of Early Psoriasis Vulgarls

�9 Dilated and tortuous capillaries in the papillary dermislZ;

�9 papillary dermal edema; �9 superficial perivascular infiltrate of lymphocyteslS; �9 slight, irregular epidermal hyperplasia in the cen-

ter of the lesion; �9 exocytosis of lymphocytes into the epidermis; �9 spongiosis in the lower levels of the epidermis; �9 focal diminution and/or disappearance of the

granular layerlg; �9 small mounds of parakeratosis in the cornified

layer overlying the foci of hypogranulosis; �9 and neutrophils at the summits of the parakera-

totic foci (early Munro microabscesses).

All are illustrated in Fig 1.

Histopathologic Features of Eruptive or Guttate Psoriasis

�9 Dilated and tortuous capillaries in the papillary dermis;

�9 marked papillary dermal edema; �9 a more pronounced perivascular inflammatory

infiltrate of lymphocytes, now with variable numbers of neutrophils2~

�9 extravasated erythrocytes in the papillary dermis and lower epidermis;

�9 slight, irregular epidermal hyperplasia; �9 exocytosis of lymphocytes into the epidermis; �9 perceptible spongiosis in the lower half of the

epidermis; �9 increased number of mitotic figures in basal and

suprabasal locations; �9 pallor of keratinocytes in the upper portions of the

epidermis; �9 focal diminution and/or disappearance of the

granular layer; �9 neutrophils forming collections in the upper spi-

nous and granular layers (spongiform pustules); �9 and dome-shaped mounds of parakeratosis with

neutrophils at their summits, alternating with orthokeratosis at different levels of a thickened cornified layer.


Hlstopathologic Features of Intermediate Psoriasis


�9 marked papillary dermal edema; �9 superficial perivascular infiltrate of lymphocytes

and neutrophils; �9 usually psoriasiform epidermal hyperplasia; �9 exocytosis of neutrophils and a few lymphocytes

into the epidermis;

A

Fig I. (A and B) Early psoriasis.


Fig 2. (A and B) Eruptive or guttate psoriasis.

�9 slight spongiosis still present in the lower levels of the epidermis;

�9 increased number of mitotic figures in basal and suprabasal locations;

�9 thinning of the suprapapillary plates; �9 pallor of keratinocytes in the upper portions of the

epidermis; �9 focal, but more extensive decrease and/or absence

of the granular layer; �9 spongiform pustules in the upper spinous and

granular layers;

�9 and focal, but more extensive areas of parakeratosis with neutrophils at their summits.


Histopathologic Features of Fully Developed Plaque Psoriasis

�9 Dilated and tortuous capillaries in the papillary dermis, that spiral to near the undersurface of the epidermis (Fig 4);

�9 massive papillary dermal edema within a thin, elongated dermal papilla (Fig 5);

Fig 3. (A and B) Intermediate psoriasis.


Jlt

Fig 4. (A, B, and C) Fully developed psoriasis.

30

�9 sparse perivascular infiltrate of lymphocytes, histiocytes, and occasional neutrophils;

�9 psoriasiform epidermal hyperplasia with elongated, thin, club-shaped rete ridges of even lengths and occasional anastomosis of neighboring rete ridges;

�9 increased number of suprabasal mitotic figures; �9 markedly thinned suprapapillary plates; �9 pallor of keratinocytes in the upper portions of the

epidermis (Fig 6); �9 diffuse decrease or absence of the granular layer; �9 spongiform pustules in the upper spinous and

granular layers 21 (spongiform pustule of Kogoj) (Fig 7);

�9 and confluent parakeratosis with collections of neutrophils arranged as tiers (Fig 8).

Histopathologic Features of Late Plaque Psoriasis

�9 Dilated and tortuous capillaries in the papillary dermis, that spiral to near the undersurface of the epidermis;

�9 decreased papillary dermal edema; �9 sparse perivascular infiltrate of lymphocytes, his-

tiocytes, and a decreased number of neutrophils;

i,!fiiii!i~ii!ii~ii!i!ii!ii~iiiii~ii!

Fig 5. Fully developed psoriasis.

ALTMAN AND KAMINO

�9 i ~ J

Fig 6. (A and B) Fully developed psoriasis.

�9 psoriasiform epidermal hyperplasia with elongated, thin, club-shaped rete ridges of even lengths and occasional anastomosis of neighboring rete ridges;

�9 decreased number of suprabasal mitotic figures; �9 markedly thinned suprapapillary plates; �9 pallor of keratinocytes in the upper portions of the

epidermis; �9 diffuse decrease or absence of the granular layer; �9 spongiform pustules in the upper spinous and

granular layers (spongiform pustule of Kogoj); �9 confluent parakeratosis with loci of orthokerato-

sis; �9 and decreased number of neutrophils within the

cornified layer.

Histopathologic Features of Verrucous Psoriasis


�9 papillary dermal edema; �9 sparse perivascular infiltrate of lymphocytes, his-

tiocytes, and occasional neutrophils; �9 papillated epidermal hyperplasia with rete ridges

of even lengths and massive hyperkeratosis; �9 increased number of suprabasal mitotic figures; �9 markedly thinned suprapapillary plates;


�9 pallor of keratinocytes in the upper portions of the epidermis;

�9 diffuse decrease or absence of the granular layer; �9 spongiform pustules in the upper spinous and

granular layers (spongiform pustule of Kogoj); �9 confluent parakeratosis with collections ofneutro-

phils arranged as tiers; �9 and may have compact orthokeratosis and verti-

cally oriented collagen bundles in the papillary dermis as evidence of persistent rubbing.


Histopathologic Features of Psoriasis on Palms and Soles


�9 papillary dermal edema; �9 may have collagen bundles in a vertical orienta-

tion in the papillary dermis, as evidence of persistent rubbing;

�9 sparse perivascular infiltrate of lymphocytes, histiocytes, and occasional neutrophils;

�9 psoriasiform epidermal hyperplasia with elongated, thin, club-shaped rete ridges of even lengths;

�9 moderate to marked spongiosis, occasionally pro- gressing to vesiculation;

�9 increased number of suprabasal mitotic figures;

F *

q

k : ,%

\ , r

" ' - 1 .

Fig 8. Munro mlcroabscess.

�9 markedly thinned suprapapillary plates; �9 pallor of keratinocytes in the upper portions of the

epidermis; �9 hypogranulosis; spongiform pustules in the upper

spinous and granular layers (spongiform pustule of Kogoj);

�9 and confluent parakeratosis with collections of neutrophils arranged as tiers.


Fig 7. Spongiform pustule of Kogoj.

Histopathologic Features of Resolving Psoriasis


�9 subtle fibrosis of the papillary dermis with increased numbers of fibroblasts22;

�9 superficial perivascular infiltrate of lymphocytes and histiocytes;

�9 psoriasiform hyperplasia of variable extent with rete ridges of even lengths;

�9 slightly thinned suprapapillary plates; �9 focal reappearance of wedge-shaped hypergranulo-

sis at the center of the rete ridges;


Fig 9. (A and B) Verrucous psoriasis.

�9 and confluent parakeratosis with compact orthokeratotic areas overlying the loci of hypergranulosis.

Differential Diagnosis of Psoriasis Vulgaris The histological differential diagnosis of psoriasis

depends on the type, stage, and site of the biopsied lesion of psoriasis. Histologically, psoriasis vulgaris must be differentiated from the other psoriasiform dermatitides. The term psoriasiform implies that the lesion either clinically or histologically mimics psoriasis. This group of disorders is characterized by the presence of parakeratosis, accompanied by a variable amount of hyperkeratosis, epidermal hyperplasia with

elongation of the rete ridges, and a superficial perivascular inflammatory infiltrate. This group includes: (1) psoriasis; (2) seborrheic dermatitis; (3) pityriasis rubra pilaris; (4) chronic spongiotic (eczematous) dermatitis such as allergic contact dermatitis, atopic dermatitis, and nummular dermatitis; (5) lichen simplex chronicus; (6) pityriasis rosea; (7) dermatophytosis; and (8) mycosis fungoides. Like psoriasis, seborrheic dermatitis is characterized by epidermal hyperplasia and neutrophils within a parakeratotic cornified layer; however, the fete ridges are of uneven lengths, there is a significant spongiosis, and the mounds of parakeratosis with neutrophils are located at the follicular ostia. Pityriasis rubra pilaris shares some histological features with psoriasis, namely, epidermal hyperplasia, pallor of the upper part of the epidermis, hyperkeratosis and parakeratosis, dilatation and tortuosity of the dermal papillary capillaries, and a superficial perivascular infiltrate. However, fully developed lesions of pityriasis rubra pilaris show broad and short rete ridges, thick suprapapillary plates, hypergranulosis, alternating parakeratosis and laminated orthokeratosis in both vertical and horizontal directions in a checkerboard fashion, follicular plugging by ortho- and para-keratotic cells, and absence of neutrophils in the cornified layer, the epidermis, or in the perivascular infiltrate. 23 Like psoriasis, chronic spongiotic (eczematous) dermatitis is characterized by epidermal hyperplasia, parakeratosis, and a superficial perivascular inflammatory infiltrate; however, it differs from psoriasis by an uneven elongation of the rete ridges, marked spongiosis, and the presence of serum admixed with parakeratotic cells in the cornified layer (scale-crust). The dermal papillae in chronic spongiotic dermatitis lack edema, but frequently contain vertically oriented collagen bundles, revealing the evidence of chronic rubbing. In addition, eosinophils, which are commonly present in allergic contact dermatitis, are rarely seen in psoriasis. Lichen simplex chronicus is characterized by prominent hyperkeratosis with focal parakeratosis, but unlike psoriasis

Fig 10. (A and B) Psoriasis vulgaris on palms and soles.


shows irregular epidermal hyperplasia with prominent hypergranulosis, vertically oriented collagen bundles in the papillary dermis, and a moderate, predominantly perivascular infiltrate of lymphocytes, histiocytes, and occasional eosinophils. 24 Pityriasis rosea, which is primarily in the differential diagnosis of early psoriasis vulgaris, shows a superficial perivascular lymphohistiocytic infiltrate with occasional eosinophils. Lympho- cytes extend into a slightly and irregularly hyperplastic epidermis, where there is spongiosis, focally decreased or absent granular layer and mounds of parakeratosis with plasma. 25 There is extravasation of erythrocytes into a slightly edematous papillary dermis with exten- sion into the epidermis. In addition to the previously mentioned features, the herald patch may show a more psoriasiform epidermal hyperplasia, greater papillary dermal edema, and a deeper and denser perivascular inflammatory infiltrate. 26 Dermatophyte infection may histologically simulate all types and stages of psoriasis. Therefore, a special stain for fungal organisms should be performed in all cases of suspected psoriasis. Derma- tophyte infection usually shows a sparse to moderate lymphohistiocytic infiltrate, occasionally with neutrophils around dilated vessels of the superficial plexus, a slight psoriasiform epidermal hyperplasia, orthokeratosis with focal parakeratosis, and the presence of fungal hyphae "sandwiched" at the interface between normal and altered (compact orthokeratosis or parakeratosis) portions of the cornified layer. 2~ Neutrophils may be

A ~

present in the altered areas of the cornified layer, within the viable epidermis, and/or in the papillary dermal perivascular infiltrate. The fungal organisms are most easily detectable near the collections of neutrophils in the ortho- rather than para-keratotic areas. 2s Intraepi- dermal pustules and vesicles may also be seen in the histological picture of dermatophytosis. Mycosis fungoides may also show a psoriasiform epidermal hyperplasia, parakeratosis in the cornified layer, and a superficial perivascular lymphocytic infiltrate. 29 However, the lymphocytes in the perivascular and band-like infiltrate and particularly those that extend into the epidermis show cytologic atypia with enlarged, hyperchromatic nuclei with irregular contors. In the papillary dermis there is fibroplasia, with collagen bundles arranged parallel to the overlying epidermis.

PUSTULAR PSORIASIS: HISTOPATHOLOGIC FEATURES

Histopathologic Features of Pustular Psoriasis


�9 papillary dermal edema; �9 superficial perivascular infiltrate of lymphocytes

and neutrophils;

Fig 11. (A and B) Pustular psoriasis.

34 I

�9 slight, irregular epidermal hyperplasia--psoriasiform hyperplasia present only in long-standing lesions;

�9 perceptible spongiosis, especially in acral sites; �9 increased number of mitotic figures in basal and

suprabasal locations; �9 and massive aggregation of neutrophils within a

lattice of degenerated keratinocytes in the upper spinous and subcorneal locations and formation of intraepidermal macropustules.

All are illustrated in Fig 11. Early lesions of pustular psoriasis on acral skin may

show spongiosis and a mononuclear cell infiltrate in the lower epidermis. 3~ This may be followed by the formation of an intraepidermal vesicle containing mostly mononuclear cells: Subsequently, as the vesicle ex- pands, neutrophils may be found scattered among keratinocytes at the periphery of the vesicle. Eventually neutrophils massively invade the cavity of the vesicle, forming a pustule.

Differential Diagnosis of Pustular Psoriasis In the differential diagnosis of pustular psoriasis are

the disorders that are characterized by intraepidermal and subcorneal pustules. The Kogoj spongiform pustule is highly characteristic of the psoriasis group of diseases, including pustular psoriasis, impetigo herpetiformis, acrodermatitis continua, geographic tongue, and Reiter's syndrome. However, spongiform pustules may also be seen in dermatophytosis, candidiasis, bacterial impetigo, pustular drug eruptions, and other pustular conditions such as early lesions of pyoderma gangrenosum and halogenodermas.

ERYTHRODERMIC PSORIASIS: HISTOPATHOLOGIC FEATURES

Histopathologic Features of Erythrodermic Psoriasis (Majority of Cases)


�9 marked edema of the papillary dermis; �9 superficial perivascular and interstitial infiltrate of

lymphocytes, histiocytes, and a few neutrophils; �9 extravasated erythrocytes in the papillary dermis

and lower epidermis; �9 slight to moderate, irregular epidermal hyperpla-

sia; �9 exocytosis of a few lymphocytes into the epider-

mis; �9 slight spongiosis in the lower levels of the epider-

mis; �9 increased number of mitotic figures in basal and

suprabasal locations; �9 pallor of keratinocytes in the upper portions of the

epidermis;

ALTMAN AND KAMINO

�9 focal decrease and/or absence of the granular layer;

�9 and mounds of parakeratosis with neutrophils. All are illustrated in Fig 12. 31

Differential Diagnosis of Erythrodermic Psoriasis

The most common causes of erythroderma include eczematous dermatitides, such as atopic dermititis and allergic contact dermatitis, psoriasis, Sezary syndrome, drug eruptions, and pityriasis rubra pilaris. In contrast to previous studies that showed that it is often difficult to distinguish the histological appearance of psoriatic erythroderma from that of chronic eczematous dermatitis, 32 Tomasini et a131 found that the histopathologic changes were specific for psoriasis in 40 of 45 patients (88%) with psoriatic erythroderma. In the majority of the patients the changes were those of early, evolving psoriasis. In erythroderma secondary to an eczematous dermatitis, there is a moderate to prominent spongiosis, parakeratosis with serum, and a superficial perivascular lymphohistiocytic infiltrate with numerous eosinophils. In erythroderma secondary to mycosis fungoides and Sezary syndrome, there is a superficial perivascular and band-like infiltrate of lymphocytes, some with irregular nuclear contours, exocytosis of atypical lymphocytes into the epidermis with minimal spongiosis, and fibroplasia of the papillary dermis. Erythrodermic drug eruptions show an interface dermatitis with vacuolar alteration of the basal layer and necrotic keratinocytes at all levels of the epidermis. In pityriasis rubra pilaris, there are alternating foci of parakeratosis and laminated orthokeratosis, thick suprapapillary plates, and an absence of neutrophils in the parakeratosis. In a certain percentage of patients with erythroderma, the etiology cannot be determined with the first skin biopsy. Repeated skin biopsies over a period of time may be necessary to make the definitive diagnosis.

Fig 12. Erythrodermic psoriasis.


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