Allergic contact dermatitis diagnosis

The clinical features of a compound allergy are those of allergic contact dermatitis. Diagnosis of a compound allergy requires the fulfillment of certain criteria ... 

Before confirming a diagnosis of subjective irritation, patients must be patch tested and open tested to exclude allergic contact dermatitis and contact urticaria, respectively. Subclinical contact urticaria, in particular, mimics sensory irritation. 

Differential diagnosis includes irritant contact dermatitis and allergic contact dermatitis. History of exposure to an offending substance assists in making the differential diagnosis. 

The most widely used topical antibiotic is neomycin. The frequency of neomycin sensitivity in the normal population in San Francisco is 1.1 % ( Prystowsky et al. 1979 b), while 5%-8% of eczema patients are allergic to neomycin. The diagnosis of allergic contact dermatitis to neomycin is difficult to make because the dermatitis is not vesicular or bullous the sensitivity often appears only as an aggravation of a pre-existing dermatitis (Epstein 1958 a). It is instructive to note that the therapeutic concentration of neomycin is often 0.5%, while the patch test concentration is 20% (Epstein 1965). 

What are the diseases under surveillance Irritant contact dermatitis, allergic contact dermatitis, atopic dermatitis. On which criteria is the differential diagnosis based ... 

Fig. 7. Allergic contact dermatitis to black rubber in a work boot. Note the hyperkeratotic scaling dermatitis most pronounced over the metatarsal area and tips of the toes. This pattern, together with sparing of the interdigital webs, the toe creases and the arch of the foot should suggest the diagnosis. Patch tests were positive to N-isopropyl-N -phenylparaphenylenediamine (IPPD) and black rubber mix. Reproduced with the permission of Donald V. Belsito, M.D., Division of Dermatology, University of Kansas Medical Center, Kansas City, KS...

A positive patch test (indicating contact allergy) is not necessarily a positive diagnosis of allergic contact dermatitis as indicated by the fact that some patients with a positive patch result never experience clinical symptoms after exposure to the test agent. The so-called COADEX classification is useful in the attempt to assess relevance of positive patch tests. COADEX stands for ... 

Nino M, Balato N, Di Costanzo L, Gaudiello F. Scratch-patch test for the diagnosis of allergic contact dermatitis to aciclovir. Contact Dermatitis 2009 60(1) 56-7. 

In a study of 1,752 patients considered to have occupational dermatoses, contact dermatitis was the main diagnosis in 1,496 patients (92% women, 83% men). The allergic type, as opposed to the irritant type, was more prevalent in men (73%) than in women (51%). Positive patch tests to chromium (not otherwise specified) occurred in 8% of the women and 29% of the men. Among 280 chromium-sensitized men, 50% were employed in building and concrete work, 17% in metal work, and 12% in tanneries. In the 42 chromium-sensitized women, 20% were in cement work, 19% in metal work, 28% in cleaning, and 15% in laboratory work (Fregert 1975). 

Tincture of iodine is a primary irritant and should be tested by the open method. Patch tests with iodine and potassium iodide may result in a nonspecific papulo-pustular reaction which must be differentiated from a contact allergic response. Patch tests with potassium iodide have been used in the diagnosis of dermatitis herpetiformis (DH) but the frequency and type of reactions expected in DH patients is neither sensitive nor specific. l,3-diodo-2-hydroxypropane, a white tincture of iodine used in Denmark for first aid, caused contact dermatitis in one patient (Hjorth 1972). He had a strong positive patch test, while 20 controls were negative. Contact allergy to iodine itself may exist, but has not been documented. 

---