Case Number : Case 1982 - 09 Jan 2018 Posted By: Dr. Richard Carr

DD: IBR, LYP, Lues ("sexy slender rete")

adding excoriation to the differential diagnosis.

Lymphoma work up not necessary?

Follicular lymphomatoid papulosis?

Given that this was a solitary lesion on the back I called it in keeping with a (lymphomatoid) lichen planus-like reaction (lichenoid keratosis). I did not do any additional work-up beyond requesting some levels and a melanA. Lymphoma is exceedingly unlikely and for me not a practical consideration.

"IBR" ?

An excoriated regressed melanocytic lesion is a great thought.  There is focal excoriation near a hair follicle (where usually insects bite) with spongiosis and exocytosis which may have been a punctum. Rarely lichenoid tissue reaction is seen in insect bite reaction. Could be a lingering IBR. 

Like the Zang and Arif comments!

my reasons for considering excoriation:

serum crust; jagged elongation of rete ridges - pseudoepitheliomatous hyperplasia; pagetoid dyskeratosis in pic 7 - related to irritation. IBR can be an underlying cause, but not necessary.

My guess is the crust is more likely what's left of whatever lesion induced the lichenoid reaction. Most frequently solar lentigo but can of course be SEBK or another superficial lesion (even melanocytic). As you say insect bites are not lichenoid and generally have eosinophils. Lymphomatoid lichenoid keratosis is the best fit and in my experience can be over-worked up for lymphoma.

What is IBR?

Insect bite reaction

Lymphomatoid lichenoid keratosis was my though too