SKINIPEDIA - Skin Studies: Psoriasis Morphologic Subtypes
Skin Encyclopedia: Clinical Spectrum and Severity of Psoriasis by
Matthew Meier & Pranav B. Sheth
Department of Dermatology, University of Cincinnati College of Medicine, Cincinnati, Ohio, USA
Inverse Psoriasis
Inverse psoriasis is characterized mainly by its distribution: it is localized predominantly
to intertriginous regions including the axillae, inframammary regions, gluteal
cleft, genitals, abdominal folds and inguinal folds. These lesions also differ in morphology
from that of typical plaque psoriasis lesions in that they are well-defined shiny
erythematous patches or thin plaques without significant scale [6, 11] (fig. 6). The
presentation may initially be confused for bacterial (often accentuated in the crease),
candidal (appearance of superficial pustules and 1- to 2-mm superficial round erosions
often helpful for diagnosis), or fungal intertrigo (less involvement of the crease,
peripheral desquamative-type scale and possible fungal involvement elsewhere, such
as the feet, gluteal cheeks, or toenails). Scrapings or cultures are sometimes needed to
discriminate between these entities.
Guttate Psoriasis
This form of psoriasis is characterized by an acute generalized eruption of smaller round
to oval-shaped well-defined erythematous scaly papules and plaques up to 1 cm in size
[12] (fig. 7). This is considered to be more of an eruptive form of psoriasis and is often
associated with infection, especially streptococcal pharyngitis [13]. More common in
children and young adults, guttate psoriasis may initially respond well to antibiotics,
heliotherapy, or phototherapy and go into remission, only to recur with reinfection.
Patients with guttate psoriasis may have a higher risk of developing plaque psoriasis
later in life. On the other hand, for some patients, guttate psoriasis may be the initial
manifestation of chronic psoriasis, triggered by infection or stress, only to evolve
into the plaque-type over time. Guttate psoriasis can also be easily confused with the
papular type of acutely flaring plaque psoriasis. The nature of the prior course, triggering
factors, and intensity of erythema and scale (less in guttate) may help in differentiating
these. Guttate psoriasis may also be confused with pityriasis rosea (PR), but
differs in the nature of the scale (psoriatic scale involves the entire lesion and is more
coarse, rather than the finer localized trailing ring pattern of the scale in PR), pattern
(psoriasis does not present in a Christmas tree pattern and is less likely to appear in
linear arrangements in the axilla and neck), and course (guttate psoriasis often lasts
longer than 8 weeks unless appropriately treated, while PR often resolves within 6–8
weeks without treatment).
Although guttate psoriasis is highly associated with streptococcal infections, there
is little evidence-based data, as documented in a Cochrane library review, to support
treatment of these patients with antibiotics [14]. In the authors’ experience, patients
with an acute papular psoriatic eruption with a throat culture positive for streptococcus
or markedly elevated antistreptolysin titers have a moderate chance of improving
and sometimes clearing their psoriasis with oral antibiotics.
Erythrodermic Psoriasis
When involvement of psoriasis becomes so diffuse that it involves more than 90% of
the total body surface area, a patient is considered to be erythrodermic. With confluence
of the lesions and diffuse involvement, the lesions may be thinner or truly flat,
and it may be difficult to identify lesions of classic plaque psoriasis. The skin may be
warm to the touch due to increased perfusion, and the nature of erythema may vary
depending on the patient’s skin color and acuity of disease (brighter red with acuity
or flaring). The scaling is also of a different quality; it is more fine, flaky, and desquamative
rather than the typical silvery coarse thick scale of plaque psoriasis (fig. 8, 9).
Of note, facial involvement may lead to ectropion.
Although not specific to erythrodermic psoriasis, as it can be seen in patients with
erythroderma of any cause, associated clinical findings may include lymphadenopathy
fever or hypothermia, tachycardia, and peripheral edema. Associated laboratory
findings can include an elevated erythrocyte sedimentation rate, hypoalbuminemia,
leukocytosis or leukopenia, anemia, and elevations of lactate dehydrogenase, liver
transaminases, uric acid, and calcium [15]. Precipitants for erythrodermic psoriasis
include the tapering or discontinuation of systemic medications (such as corticosteroids,
cyclosporine, or methotrexate), phototherapy-related toxicity, irritants (such as
tar), and systemic illness or infection. Significant morbidity may occur due to dehydration
from extensive fluid and electrolyte disturbances, protein losses, high-output
cardiac failure, and infection.
Psoriasis is only one of many causes of erythroderma. Cutaneous T cell lymphoma
– typically in the setting of Sezary syndrome, atopic dermatitis, drug reactions, other
papulosquamous skin diseases (such as pityriasis rubra pilaris), as well as connective
tissue diseases such as lupus or dermatomyositis among others – can also present as
exfoliative erythroderma. Presence of classic cutaneous, scalp, or inverse lesions, nail
findings, or personal or family history of psoriasis may provide clues to the etiology
of erythroderma [16]. Skin biopsies are often unhelpful in confirming erythroderma
secondary to psoriasis, but may be helpful in ruling out cutaneous T cell lymphoma
or connective tissue disease.
Small Plaque Psoriasis
This form of psoriasis is similar in morphology to guttate psoriasis with discrete papules
and plaques, with lesions as large as 3 cm in size. However, small plaque psoriasis
represents a chronic form of psoriasis rather than an acute eruptive process [12]. This
variant may not have the pattern of accentuation on the extensor extremities, scalp,
elbows, and knees as in classic psoriasis, and may have a more randomly distributed,
scattered, and diffuse pattern.
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