Which histologic findings are characteristic of polymorphous light eruption (PMLE)?

Updated: Jan 22, 2020
  • Author: Saud A Alobaida, MBBS, FRCPC; Chief Editor: Dirk M Elston, MD  more...
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Answer

The most striking feature of the biopsy specimen from a patient with polymorphous light eruption (PMLE) is edema in the upper part of the dermis. Tight, perivascular lymphocytic infiltrate is observed in the upper and mid dermis. When eczematous epidermal changes are present clinically, spongiosis, edema, dyskeratosis, and basal cell vacuolization may be observed. Occasionally, neutrophils and eosinophils may be present in the infiltrate. The dominant cell, however, is the lymphocyte. Mucin, which is thought to distinguish PMLE from lupus, can be present in skin biopsies of PMLE patients. A study of dermal mucin from lupus samples found that it is not so much different from that found in PMLE in comparison with other dermatitides, which also had some, but less, mucin (eg, erythema multiforme, fixed drug eruption, graft versus host disease, lichen planus, photodamaged skin). [46] Erythema multiforme subtype can show evidence of a vacuolar interface with liquefactive degeneration of the dermoepidermal junction. A predominantly neutrophilic subtype also can be seen, which may be confused with Sweet syndrome. Chilblains has similar pathological features, but the history and location of the lesions can usually help make the diagnosis.

Note the images below.

Polymorphous light eruption pathology showing papi Polymorphous light eruption pathology showing papillary dermal edema. Courtesy of DermNet New Zealand (https://www.dermnetnz.org/assets/Uploads/pathology/e/pmle-figure-1.jpg).
Polymorphous light eruption pathology showing papi Polymorphous light eruption pathology showing papillary dermal edema. Courtesy of DermNet New Zealand (https://www.dermnetnz.org/assets/Uploads/pathology/e/pmle-figure-2.jpg).
Polymorphous light eruption pathology showing papi Polymorphous light eruption pathology showing papillary dermal edema with lymphocytes in the epidermis (exocytosis). Courtesy of DermNet New Zealand (https://www.dermnetnz.org/assets/Uploads/pathology/e/pmle-figure-3.jpg).
Polymorphous light eruption pathology. The infiltr Polymorphous light eruption pathology. The infiltrate is mainly lymphocytic but there may be intermixed eosinophils, neutrophils, and histiocytes. Courtesy of DermNet New Zealand (https://www.dermnetnz.org/assets/Uploads/pathology/e/pmle-figure-4.jpg).

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