Red Alert or Red Herring?

The role of eosinophils in the differential diagnosis of inflammatory skin diseases

Eosinophils are known to be present in inflammatory skin diseases, but their diagnostic utility is not well established. Upon review of the published status of lesional eosinophils, several categories were identified. 1) Lesional eosinophils highly characteristic such that, in their absence, the pathologist may question the diagnosis. These include arthropod bite reactions and scabies, urticarial dermatitis, and other eosinophilic dermatoses. 2) Lesional eosinophils rare or absent, such that, in their presence, the pathologist may question the diagnosis. These include pityriasis lichenoides, graft versus host disease, and connective tissue disorders. 3) Lesional eosinophils variable and, while in some cases expected, are not required for diagnosis. These include drug reactions, atopic dermatitis and allergic contact dermatitis. 4) Lesional eosinophils variable and not expected but may be seen to a limited extent. These include lichen planus and psoriasis.

Eosinophil-rich syphilis: a report of four cases

The differential diagnosis for eosinophil-rich skin lesions often includes a drug reaction, allergic contact dermatitis and rarely, response to a helminth infection. However, many unrelated entities, such as infections, neoplasms and inflammatory dermatoses, can have a prominent eosinophilic infiltrate. Syphilis is classically associated with plasma cells, but other patterns of inflammation have been reported, including ulcerative, granulomatous and eosinophil-rich. Classic teaching might indicate that the presence of eosinophils argues against a diagnosis of syphilis. We present four cases of secondary syphilis with increased eosinophils, ranging from 8 to >200 eosinophils per 10 high-power fields (×400 magnification). Patient 1 had lesions on the penis and scrotum, with greater than 200 eosinophils per 10 high-power fields. Patient 2 had lesions on the back, with 150 eosinophils per 10 high-power fields. Patient 3 had lesions on the bilateral arms, with 8 eosinophils per 10 high-power fields. Patient 4 had lesions involving the anus, with 17 eosinophils per 10 high-power fields. These cases highlight that the presence of an eosinophil-rich infiltrate on skin biopsy should not exclude syphilis from the differential diagnosis.

Eosinophils in biopsy specimens of lichen sclerosus: a not uncommon finding

BACKGROUND

Evolving lesions of lichen sclerosus (LS) pose a diagnostic challenge owing to an absence of classic findings of epidermal atrophy, dermal sclerosis, a band-like lymphocytic infiltrate and the presence of eosinophils.

METHODS

Retrospective specimens of LS were reviewed. Demographic information, biopsy vs. excision and the following histopathological characteristics were noted: presence and number of eosinophils, epidermal hyperplasia, spongiosis, early/transitional LS, well-developed LS and coexisting squamous cell carcinoma (SCC). Linear regression analysis was performed.

RESULTS

The data consisted of 66 biopsies (36 male [M], 30 female [F]), from 53 individuals (33M, 20F), including 57 genital and 9 extragenital biopsies. Seven biopsies showed SCC, 28 showed epidermal hyperplasia and 14 exhibited spongiosis. Thirty-five specimens were early/transitional LS and commonly exhibited epidermal hyperplasia (57%), epidermotropism of lymphocytes (97%) and basement membrane thickening (97%). Thirty-five biopsies (53%) contained eosinophils (23 early/transitional lesions). Male gender (p = 0.074) was associated with increased eosinophils. The presence of SCC (p = 0.014) was a significant predictors of eosinophil number.

CONCLUSIONS

Epidermal hyperplasia, epidermotropism of lymphocytes and basement membrane thickening are helpful features in identifying early LS. Eosinophils are not an uncommon finding in LS and are most common in male genital lesions and in LS associated with SCC.