Eritema multiforme fotodistribuido

Photodistributed Stevens-Johnson syndrome and toxic epidermal necrolysis: a systematic review and proposal for a new diagnostic classification

BACKGROUND

Ultraviolet radiation (UVR) exposure is commonly reported as a risk factor for Stevens-Johnson syndrome (SJS) and toxic epidermal necrolysis (TEN). However, minimal evaluation of photo-induced SJS/TEN has been conducted. Thus, this review identifies all cases of SJS/TEN that are linked to an acute exposure of UVR and outlines the unifying characteristics of these cases. Furthermore, the theoretical pathogenesis, differential diagnoses, and proposed diagnostic criteria are defined.

METHODS

PubMed, Google Scholar, and other databases and websites were searched from inception to September 2021 to identify studies that met inclusion criteria. The following keywords were utilized: "Stevens-Johnson syndrome" and "toxic epidermal necrolysis" with "ultraviolet," "photodistributed," "photo-induced," "photosensitivity," and "photo." One reviewer assessed study characteristics, with confirmation by a second. The risk of bias was assessed independently by another.

RESULTS

Thirteen patient cases were identified, all reporting ultraviolet radiation prior to rash onset and an underlying causal drug. Case classifications included 7/13 SJS and 6/13 TEN. All cases described the rash as photodistributed with UVR exposure prior to rash onset (delay of 1-3 days) and a causal drug. 10 cases provided evidence that the photodistributed rash lacked linear demarcation (as in a sunburn) with satellite target-like lesions. No cases described a flu-like prodrome.

DISCUSSION

Mucositis, palmar and plantar rash, a positive Nikolsky sign, and a prolonged disease course can help distinguish from photosensitive reactions, while a negative direct immunofluorescence test is important to distinguish from other photo-induced disorders.

CONCLUSION

Physicians should be aware that UVR may precipitate SJS/TEN in patients taking susceptible drugs. After a 24-h delay from UVR exposure, a non-distinct, photodistributed rash appears with no flu-like prodrome and progresses for at least 48 h to include vesiculobullous eruptions and mucous membrane involvement. Photodistributed SJS/TEN appears to be photo-drug-induced with a unique onset and rash presentation that should be recognized as a distinct diagnosis.

A retrospective review of hyperaesthetic leucotrichia in horses in the USA

BACKGROUND

Hyperaesthetic leucotrichia (HL) rarely affects horses and causes painful lesions on the dorsum that result in leucotrichia. This may be a variant of erythema multiforme (EM), but there are no studies investigating this condition.

OBJECTIVES

Describe the clinical and histological features of HL and compare them to the histological features of EM.

METHODS

A retrospective review of medical records from 1985 to 2015 identified 15 horses with HL. Thirteen biopsies of HL and five of EM were evaluated and compared.

RESULTS

Arabian horses and their crosses (χ(2) (1)  = 8.56, P < 0.01) and American paint horses (χ(2) (1)  = 6.64, P < 0.05) were over represented. The onset of clinical signs was between April and September (14 of 15). The most common clinical signs were pain (15 of 15), leucotrichia (11 of 15), crusting (10 of 15) and alopecia (8 of 15) limited to darkly pigmented skin. The lesions recurred seasonally in 6 of 12 horses and unpredictably in 1 of 12 horse. The most common histological features were the presence of large stellate cells (13 of 13) and oedema (12 of 13) in the superficial dermis, perivascular to diffuse lymphocytic inflammation (13 of 13), pigmentary incontinence (12 of 13), apoptotic keratinocytes (9 of 13) and vesicle formation (8 of 13). Horses with EM (n = 5) had significantly more acanthosis (z = -2.40, P < 0.02) and lymphocytic exocytosis (z = -3.1, P < 0.004), satellitosis (Fisher's exact P = 0.02) and inflammation (z = -2.91, P < 0.004). Horses with HL had significantly more pigmentary incontinence (z = 2.13, P < 0.04) and superficial dermal oedema (z = 2.56, P < 0.002).

CONCLUSIONS

HL affects primarily Arabian horses and American paint horses. It occurs mainly in summer and may recur. Histologically HL shares features with EM, but there are significant differences between them.