Case Number : Case 2758 - 1 February 2021 Posted By: Richard Logan

Some visitors in the stratum corneum?!

Episodic visitors!

I don't know. let me wait for the answer

? Fungal infection. Xerotic eczema..acquired ichthyiosis..

I know erythrasma on flexural regions...so I don’t know what it could be. Waiting for the answer. 

This is a case from my archives from about 20 years ago.  At that time there was a small outbreak of irritant contact dermatitis due to exposure mainly to the antiseptic agent benzalkonium chloride.  This was present at a concentration of 6% in a bath emollient commonly prescribed at that time.  Most of the cases therefore occurred in patients with eczema whose barrier function was impaired and who were at greater risk of this complication.

Patients typically developed a reddish-brown, dry, hyperkeratotic eruption especially in body folds or at other sites exposed to the benzalkonium (see clinical picture).

Histologically the changes are confined to the stratum corneum with little or no underlying inflammation.  This has been described as "granular parakeratosis" although I must admit that the parakeratosis is not well reproduced in these slides.

Your suggested alternative diagnoses are all very sensible.  I presented this case to illustrate an example of "top heavy" histology which should always suggest an exogenous cause.

A relevant report was by Saw NK and Hindmarsh JR: Postgrad Med J 2005;81:131–132. doi: 10.1136/pgmj.2003.018564