Pityriasis Lichenoides: A Large Histopathological Case Series With a Focus on Adnexotropism

Abstract

Introduction: Pityriasis lichenoides (PL) is an infrequent skin disorder. The clinical manifestations are usually specific enough for a reliable diagnosis, although the histopathological assessment of a biopsy is sometimes needed to differentiate between PL and a range of other diseases. The objectives of this study were to review cases of PL managed in our hospital, confirm the classical histopathological features of PL, and identify signs that may be of value in the diagnosis of PL. Materials and Methods: All cases of PL assessed in our pathology department between January 2007 and December 2017 were retrieved, and all slides were reviewed. Cases were selected only if a diagnosis of PL was initially suggested by a dermatologist and then confirmed by the histopathological assessment. Results: Seventy-one cases met the study criteria. The following features were almost always present: vacuolar changes or necrotic keratinocytes (100%), both superficial and deep lymphocytic infiltrates (99%), and the infiltration of lymphocytes into the adnexal epithelium (97%). The inflammatory cells were always small- to medium-sized lymphocytes. There were no eosinophilic infiltrates. Superficial perivascular and/or intraepidermal red blood cells were observed in 83% of cases. Discussion: We highlighted the presence of a deep dermal lymphocytic infiltrate, with a “T-shaped” periadnexal arrangement along the full length of the follicular and sudoral epithelia. This might be a feature that enables the differentiation of PL from other diseases. Our findings also prompted a number of physiopathological hypotheses for PL. Conclusions: Our present results confirmed the classical histological aspects of PL and provided some useful new diagnostic features.

Comment on “Histopathologic features distinguishing secondary syphilis from its mimickers”

“…The infiltrate has a T-shaped aspect or-when several adnexal structures are involved-an African-tree aspect. 2 In our opinion, this feature is highly suggestive of PL and has never been described in syphilis. Finally, the inflammatory infiltrate in PL is primarily composed of lymphocytes and contains few plasma cells.…”

“…However, in cases of PL, the presence of necrotic keratinocytes, particularly in the upper epidermis (observed in 100% of our cases of PL), pallor of the upper epidermis (42%), red blood cell extravasation (83%), and intraepidermal erythrocyte exocytosis (32%) may be useful clues. With regard to dermal changes, interstitial inflammation may be observed in cases of PL (as mentioned by Flamm et al), [1][2][3] but it is always associated with perivascular and periadnexal inflammation. In our opinion, a deep dermal lymphocytic infiltrate (in addition to a superficial infiltrate) is a very frequent sign of PL.…”

Pseudomalignancies in Children: Histological Clues, and Pitfalls to Be Avoided

“…However, some findings tend to indicate a diagnosis of PL: an intra-epidermal lymphocytic infiltrate associated with necrotic keratinocytes, cellular monomorphism with a complete absence of eosinophils, and few or no large lymphoid cells. Furthermore, our recent study showed that the lymphocytic infiltrate is usually wedge-shaped in LyP (except for the recently described follicular variant) but is T-shaped and follows the adnexa in PL [8]. Some cases of PL are difficult to distinguish clinically from lymphomatoid papulosis (LyP); this is notably the case when the lesions are necrotic and few in number.…”

“…Moreover, PL can be present before (or at the same time as) MF in children. The histological picture in PL usually includes parakeratosis, epidermal hyperplasia, variable numbers of necrotic keratinocytes, interface changes with prominent lymphocytic exocytosis, perivascular, and periadnexal lymphocytic infiltrates in the superficial and deep dermis, and red blood cell extravasation [8]. However, some cases present with prominent intra-epidermal lymphocytes, basal cell replacement by lymphocytes, and nuclei surrounded by a clear halo-as in MF (Figure 3).…”

Adnexotropic Variants of the Interface Dermatitides: A Review

“…It was also found that a denser periadnexal inflammation was observed in PLEVA/PLC overlap cases. This pattern of adnexotropism prompted the authors to suggest the descriptive term of a "T-shaped" inflammatory cell infiltrate, rather than a wedge-shaped infiltrate [37]. Syringotropic lymphocytes has been reported in one case of acral pityriasis lichenoides [38].…”