Fig. 35.1
Left panel demonstrates a pregnant woman with generalized eruption of red papules characteristic of pruritic urticarial papules and plaques of pregnancy. Right panel demonstrates an old man with idiopathic, severely pruritic papules that he excoriates. Histological examination of a rare primary lesion revealed the findings of hypersensitivity reaction or prurigo simplex
Case
A patient presents with itchy, red papules scattered over the trunk and/or extremities. Some or many lesions may be excoriated. Only a rare lesion may be lichenified, appearing as prurigo nodularis. New lesions appear at variable intervals, and each lesion may last for a few days to few weeks.
The quality of life of most patients who present as above is compromised and many have been to allergists and/or a few dermatologists expecting an answer as to the cause of the lesions and/or a cure. Some may have diagnosed themselves as allergic to something or another, and others have declared themselves or were told to be gluten-sensitive. Most of them are resistant to topical steroids including superpotent ones. Most patients respond dramatically to systemic steroids.
The differential diagnosis of the above presentation includes:
A. Disorders with identifiable etiology such as:
Insect bite reaction, including mites and pediculosis
Scabies
Drug eruption
“Neutrophilic dermatosis” secondary to any of multiple systemic disorders , and
B. Disorders without identifiable etiology, namely, the idiopathic disorder(s) that has been named at different times, in different countries, and by different authors as prurigo simplex, subacute prurigo, prurigo mitis, “itchy red bump disease” , and hypersensitivity reaction.
In the evaluation of these patients, two groups of disorders should be excluded, namely:
Patients with generalized pruritus and excoriations without primary lesions (discussed in Chap. 27)
Patients with delusions of parasitosis and secondary excoriations, without primary lesions
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