#dermpathJC September 2020:
Thursday, September 24th, 9 pm EST
Article Discussed: Pityriasis Lichenoides: a large histopathological case series with a focus on adnexotropism
Authors: Menzinger, Sébastien MD, Frassati-Biaggi, Annonciade MD, Leclerc-Mercier, Stéphanie MD, Bodemer, Christine MD, PhD, Molina, Thierry Jo MD, PhD, Fraitag, Sylvie MD
Temporary free access courtesy of American Journal of Dermatopathology: https://doi.org/10.1111/cup.13585
Summary prepared by: Riddhish Sheth, MD (@RShethMD)
Journal Club Summary:
Pityriases lichenoides (PL) is a rare skin disorder, the acute form of which is predominantly seen in children and young adults (PLEVA – pityriasis lichenoides et varioliformis acuta) and a milder, more chronic form (PLC – pityriasis lichenoies chronica), more often seen in adults. There is also a severe form known as febrile ulceronecrotic Mucha-Habermann disease.
PLEVA histologically presents with epidermal hyperplasia with parakeratosis and neutrophils in the stratum corneum, dyskeratotic keratinocytes, interface dermatitis, lymphocytic exocytosis, dermal perivascular lymphocytic infiltrate, and red blood cell (RBC) extravasation. PLC is described to have much milder changes. There are cases where the histological features are incomplete or lack specificity which can lead to misdiagnosis of a lymphoproliferative disorder such as Lymphomatoid Papulosis (LyP).
71 cases were investigated in this case series. The authors noticed that vacuolated, necrotic keratinocytes were present in all cases, superficial and deep lymphocytic infiltration was present in 99% of cases, and adnexal lymphocytic infiltration was present in 97% of cases. They noted that the inflammatory cells were mostly lymphocytes, neutrophils were only present in cases with ulceration of the superficial dermis, and that there were no eosinophils histologically identified in any of the study’s cases. The authors also noted that 83% of cases showed perivascular or intraepidermal RBCs, and that 42% of cases had pallor of the upper part of the epidermis. The authors alluded to Dr. Ackerman and his description of Pityriasis Lichenoides which included the superficial epidermal pallor but stated that this sign was not always easy for them to evaluate because it may be technique dependent.
Immunohistochemical (IHC) studies were also performed on 11 cases at random and there was no IHC staining profile pattern which they found that would be reliable to aid in the diagnosis of the Pityriasis Lichenoides.
To go back to the adnexotropism mentioned earlier, the authors conclude that the superficial and deep dermal lymphocytic infiltrate is arranged in a periadnexal manner and it manifests as a “T-shaped” infiltrate which can be a low power clue in the diagnosis of Pityriasis Lichenoides. They compared this low power pattern of the lymphocytic infiltrate to Vachellia tortilis, an African thorn acacia tree. This was seen in 97% of the cases in this series.
Vasculitis or eosinophilic infiltrates are not a feature of Pityriasis Lichenoides. Furthermore, in this case series, there were no histologic differences present between the specimens of adults and children.
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