Up Close: A Look at Dermatological Diagnoses

Up
Close
A Look at Dermatological Diagnoses
by Catherine McCuaig, MD, FRCPC
Université de Montréal
Psoriasis and Eczema
How do I accurately differentiate
psoriasis from eczema?
Table 1
Trigger factors contributing to psoriasis
• genetics: up to 50% have positive family
It is usually easy to distinguish psoriasis from dermatitis, however not always. Both are chronic erythematosquamous skin conditions.
In the patient’s history, trigger factors contributing
to psoriasis are listed in Table 1. In addition to these
factors, 20% to 34% of patients with psoriasis have a
seronegative, usually oligo- or polyarticular arthritis.
On physical examination, the clinical differentiation
from dermatitis will depend on the type of psoriasis.
The most common form of psoriasis is chronic
plaque type with thick well-circumscribed plaques
much thicker than what is seen in eczema.
There is a form of neurodermatitis called lichen
simplex chronicus which presents with well-circum-
Dr. McCuaig is an associate professor,
Université de Montréal, and
dermatologist, department of
pediatrics, Hôpital Ste. Justine,
Montreal, Quebec.
history of psoriasis (increased HLA-Cw6)
• medications: beta blockers, lithium, nonsteroidal
anti-inflammatories, withdrawal of corticosteroids
• recent infection: Streptococcal pharyngitis or
perianal dermatitis
• trauma
• stress
scribed plaques, caused by chronic rubbing or scratching. The history in these cases will be critical. In most
cases, the plaque will be solitary and unilateral. The
symmetric distribution of plaques on the extensor surfaces of the elbows, knees, trunk, and scalp are classic
symptoms of psoriasis.
In the scalp and intertriginous areas of infants, and
the scaling of the scalp and eczematous patches on the
forehead and nasolabial folds of adults, seborrheic dermatitis may be difficult to clearly distinguish from
psoriasis (hence the term sebopsoriasis).
The Canadian Journal of CME / June 2003 55
Up Close
Inverse psoriasis may be found in
patients who also have plaques, or in the intertriginous areas alone. Bright red well-circumscribed patches are found in the groin, axilla,
gluteal fold, and inframammary areas.
The guttate form of psoriasis presents often in
young patients, preceded by strep pharyngitis,
perianitis, or sunburn. An eruption on the trunk
and proximal extremities with fine, oval, 1 cm
scaling patches evokes a differential diagnosis of
pityriasis rosea, more than nummular eczema.
Localized pustular psoriasis on the palms
and soles may mimic dyshidrotic eczema, but
usually the pustules are larger in psoriasis, and
the background erythematous patch is more
sharply marginated.
Figure 1. Psoriatic fingernail changes.
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Mai 2003
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Volume 18, numéro 5
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21 Frequently Asked Questions
Voir page 71
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Up Close
The erythrodermic patient with generalized erytheTable 2
ma may have dermatitis, psoriasis, drug eruptions, neoClassic psoriasis pathology
plasia, or idiopathic.
• thickening of the epidermis (acanthosis) with clubNails changes with oil-drop changes, and subungual
shaped rete ridges
hyperkeratosis are further characteristics of psoriasis;
pitting, strations, splinter hemorrhages, and onycholysis
• thickening of the stratum corneum with parakeratosis
may also be found in cases of eczema (Figure 1).
• neutrophilic infiltrate through the epidermis
Of course, skin biopsy can be performed when in
• spongiform pustules of Kogoj
doubt. The classic pathology for psoriasis is described
• papillary edema with dilated tortuous blood vessels
in Table 2.
Both dermatitis and psoriasis have a perivascular
lymphocytic infiltrate, with intracellular edema of the
epidermis (spongiosis). This also occurs in cases of
acute dermatitis. CME