An itchy localized eruption



A 59-year-old bus driver presents with a 5-month history of a persistent itchy patch
below his umbilicus. Initially it began as an intermittent eruption, coming and going in
an apparently random pattern; over the past six weeks, since the weather became warmer,
it has persisted. He is otherwise well with no history of previous skin problems. He is not
on medication.
There is a localized area of marked lichenification, post-inflammatory hyperpigmentation,
excoriation and erosion at the midline below his umbilicus (Fig. 7.1). The surrounding
skin has a more diffuse area of low-grade lichenification, hyperpigmentation and
mild erythema

• What could this eruption be?
• How should he be investigated?
• What information does this man need?

These lesions are best described as chronic and eczematous. Such a localized problem
suggests an exogenous aetiology (the photograph that is Fig. 7.1 provides a clue). The
most likely diagnosis is allergic contact dermatitis (ACD), although it can be very difficult
to differentiate clinically between ACD and irritant contact dermatitis. Occasionally,
psoriasis may present with a single plaque, particularly at a site of trauma (Koebner’s
effect); however, it is rarely as pruritic as this eruption. Atopic dermatitis is usually
a more generalized and diffuse eruption; however discoid or nummular eczema is
characterized by fairly well defined, coin-shaped, intensely pruritic inflamed areas of
lichenified skin. An inflammatory tinea corporis particularly associated with a zoophilic
organism might also be considered. The presentation of contact dermatitis can be varied,
including dyspigmentation, pustular lesions, urticaria, atrophy, phototoxic reactions and
It would be appropriate to obtain a skin scraping for mycology investigations. Patch
testing (Fig. 7.2) is the diagnostic test to detect sensitization to contact allergens.
(Although patch testing is not required for diagnosis; nickel allergy is one of the
few types of allergic contact dermatitis where the history of exposure along with
the signs and symptoms are quite distinctive.) In fact many patients do not present
to medical practitioners as they may well work out the association themselves. If a
patch test series confirms the presence of nickel allergy, its relevance to the current
eruption should be confirmed. A dimethylglyoxime (DMG) test is a simple, inexpensive
way to determine whether the object in question contains nickel by a pink colour
change. Chromate, palladium and cobalt are commonly found together with nickel and
concomitant allergy may coexist.
Nickel is a leading cause of allergic contact dermatitis and is responsible for more cases
than all other metals combined. Certain occupations with high exposure to nickel, such
as cashiers, hairdressers, metal workers, domestic cleaners, food handlers, bar workers,
and painters, are also at risk for acquiring nickel dermatitis. Patients with atopic
eczema are also at increased risk. Sweating may increase the severity of the dermatitis.
Sodium chloride in the sweat causes corrosion of the metal and increases nickel
The management of this case includes removal of the offending nickel-containing belt
buckle or trouser rivet and application of topical corticosteroid creams until the eruption
has resolved. The patient also requires information about his allergy, that is he will
always remain allergic to nickel and to both the common and unexpected sources of
nickel. Nickel allergy is commonly associated with earrings and jewellery or other body
piercing. Nickel can be found in many everyday items – from coins to necklace clasps,
from watchbands to eyeglass frames, and tools and utensils used in the workplace and