Discussion
Cobalt is an ingredient of vitamin B12 or cobalamin, reaction to cobalt
may cause problems in patients receiving vitamin B12 replacement
therapy. Several cutaneous manifestations have been reported in patients
with allergic contact dermatitis to cobalt undergoing oral cobalamin
replacement including atopic dermatitis, chronic vesicular hand
dermatitis, cheilitis, and stomatitis. (4)
Systemic contact dermatitis (SCD) is a condition occurring in previously
sensitized individuals after systemic re-exposure to the same or
cross-reacting substance. Sensitization occurs due to varying exposures
to antigens via multiple routes through the circulatory system, and
thereby produces systemic allergic dermatitis, which may result in a
variety of skin eruptions and systemic flare. The exact mechanisms
behind SCD are not fully understood, but is thought to be a T-cell
mediated delayed type hypersensitivity reaction. (5) The common
allergens inducing systemic contact dermatitis include nickel, zinc and
cobalt. (6-8) Several systemic agents are associated with pigmentation
including cytotoxic agents, antimalarial, analgesics and silver but
pigmented systemic contact dermatitis after intake of cobalt containing
diet has never been reported.
Osmundsen et al. first described pigmented contact dermatitis (PCD) as a
non-eczematous variant of contact dermatitis, clinically characterized
by hyperpigmentation with little or no signs of dermatitis by
observations that the melanosis was due to contact dermatitis caused by
an optical whitener containing pyrazoline present in a washing powder.
(9) The exact mechanism which allergens induce hyperpigmentation remains
unknown. Some experimental studies have shown that allergens having a
special affinity for melanin induced cutaneous inflammation increasing
the number and size of the melanocytes and enhancing their enzymatic
activity (9, 10). The common allergens responsible for pigmented contact
dermatitis are listed in Table 1. Related studies have demonstrated
cases of pigmented contact dermatitis and histopathological examination
revealed focal vacuolar degeneration of the epidermis and increased
dermal melanophages with superficial perivascular lymphocytic
infiltration. (11, 12) Although the exact mechanism of how cobalt
induces systemic contact dermatitis remains unknown (13), one related
study revealed the increasing prevalence of cobalt allergy in the
general population and the high popularity of food supplements
containing cobalt, e.g., vitamin B12 supplement. (14)