Case Number : Case 734 - 9 Apr Posted By: Guest

Lichen planus, despite the presence of some eosinophils.

This is a solitary lesion. Perhaps a much better diagnosis is a lichen planus like keratosis. This would explain the eosinophils.

Lichenoid keratosis

lichenoid interface dermatitis consistent with Lichen Planus and with the eosinophils consider lichenoid drug reaction.

Lichenoid keratosis vs LP- CPC required.

Lichenoid dermatitis with discrete foci of parakeratosis and some necrotic keratinocytes. Frequent eosinophils and rare plasma cells are also found in the lymphocytic predominant infiltrate.
I favor lichen planus-like drug eruption.

Reading my colleagues opinions, I found lichen planus-like keratosis (aka lichenoid keratosis). I think, however, this represent a solar lentigo undergoing regression and, for this very reason, its preferred location is a sun-exposed site.
Am I correct?

The lesion being described as single will favor lichen planus like keratosis. Esinophils are seen in LPLK. Of course on seeing esinophils in this context one will think first in lichenoid drug reaction but I have never seen solitary lesions of lichenoid drug reaction.

LPLK for sure based on solitary lesion

LPLK.

Lichenoid keratosis.

In answer to Dr Rocha's question "LPLK" is not a diagnosis it is a reaction pattern.
Solar lentigo is possibly the most common association but it is basically a lichenoid reaction to a superficial lesion the nature of which almost by definition is uncertain. It could be seen in reaction to pre-existing actinic keratosis, thin seborrhoeic keratosis, thin SCC and indeend thin melanoma. Some pathologists recommend examination of multiple levels in all cases and I have heard some experts stating that a MelanA should be done on all cases. I am very wary about making the "diagnosis" of LPLK in a partial specimen e.g. punch biopsy and I emphasise it is a non-diagnosis / reaction pattern. Obviously if there is any clinical concern about a lesion it should be excised with clear margins in such cases. My comments may be conservative but unfortunately I have myself missed a thin melanoma (on punch biopsy due to brisk inflammatory reaction) that had very sparse histiocyte-like dermal cells and unfortunately the same lesion was punch biopsied a year latter and reported by another pathologist as LPLK (when on review there was more obvious SSMM). The final diagnosis of melanoma was delayed for two years in that particular case. All that said I don't personally automatically do MelanA myself on all cases I am very selective but I do automatically examine multiple levels in an attempt to make a specific diagnosis.

Thanks Dr Carr for the valuable comment.

Thank you, Dr. Carr, for your kind and enlightening comment.