[Limbal stem cell deficiency management. A review]

Ocular sequelae of epidermal necrolysis: French national audit of practices, literature review and proposed management

Stevens-Johnson Syndrome (SJS) and toxic epidermal necrolysis (TEN) are serious and rare diseases, most often drug-induced, and their incidence has been estimated at 6 cases/million/year in France. SJS and TEN belong to the same spectrum of disease known as epidermal necrolysis (EN). They are characterized by more or less extensive epidermal detachment, associated with mucous membrane involvement, and may be complicated during the acute phase by fatal multiorgan failure. SJS and TEN can lead to severe ophthalmologic sequelae. There are no recommendations for ocular management during the chronic phase. We conducted a national audit of current practice in the 11 sites of the French reference center for toxic bullous dermatoses and a review of the literature to establish therapeutic consensus guidelines. Ophthalmologists and dermatologists from the French reference center for epidermal necrolysis were asked to complete a questionnaire on management practices in the chronic phase of SJS/TEN. The survey focused on the presence of a referent ophthalmologist at the center, the use of local treatments (artificial tears, corticosteroid eye drops, antibiotic-corticosteroids, antiseptics, vitamin A ointment (VA), cyclosporine, tacrolimus), the management of trichiatic eyelashes, meibomian dysfunction, symblepharons, and corneal neovascularization, as well as the contactologic solutions implemented. Eleven ophthalmologists and 9 dermatologists from 9 of the 11 centers responded to the questionnaire. Based on questionnaire results, 10/11 ophthalmologists systematically prescribed preservative-free artificial tears, and 11/11 administered VA. Antiseptic or antibiotic eye drops or antibiotic-corticosteroid eye drops were recommended as needed by 8/11 and 7/11 ophthalmologists, respectively. In case of chronic inflammation, topical cyclosporine was consistently proposed by 11/11 ophthalmologists. The removal of trichiatic eyelashes was mainly performed by 10/11 ophthalmologists. Patients were referred to a reference center for fitting of scleral lenses (10/10,100%). Based on this practice audit and literature review, we propose an evaluation form to facilitate ophthalmic data collection in the chronic phase of EN and we also propose an algorithm for the ophthalmologic management of ocular sequelae.

Panorama of limbal changes

The corneal limbus is a privileged region on the border between two quite different microenvironments, where corneal epithelial stem cells, numerous melanocytes, and antigen-presenting cells are all concentrated within a richly vascularized and innervated stroma. This situation within the ocular surface confers on it the key functions of barrier, epithelial renewal and defense of the cornea. As an immunological crossroads and since the corneoscleral limbus is directly exposed to external insults such as caustic agents, ultraviolet radiation, microbial agents, and allergens, it is the potential site of many tumoral, degenerative or inflammatory pathologies and may progress under certain conditions to limbal stem cell deficiency.

Corneal keratin aggresome (CKAGG) formation and clearance by proteasome activation

Purpose

To understand the mechanism of corneal keratin expression and clearance in corneal epithelium with Limbal Stem Cell Deficiency (LSCD). The hypothesis is that LSCD-induced proteasome dysfunction is a contributing factor to keratin aggregation, causing corneal keratin aggresome (CKAGG) formation.

Method

LSCD was surgically induced in rabbit corneas. LSCD corneal epithelial cells (D-CEC) were collected to investigate keratin K4 and K13 expression and CKAGG formation. Oral mucosal epithelial cells (OMECS) were isolated and cultured to study K4 and K13 expression. Cultured cells were treated with proteasome inhibitor to induce CKAGG formation.

Results

K4 and K13 were strongly expressed in D-CEC, with additional higher molecular weight bands of K4 and K13, suggesting CKAGG formation. Double staining of K4/K13 and ubiquitin showed co-localization of these keratins with ubiquitin in D-CEC. Proteasome inhibition also showed K4/K13 modification and accumulation in cultured OMECS, similar to D-CEC. Proteasome activation was then performed in cultured OMEC. There was no accumulation of keratins, and levels of unmodified keratins were found significantly reduced.

Conclusion

Results showed an abnormal expression of K4 and K13 after LSCD-induced proteasome dysfunction, which coalesce to form CKAGG in Corneal Epithelial Cells (CEC). We propose that CKAGG formation may be one of the causative factors of morphological alterations in the injured corneal epithelium, and that CKAGG could potentially be cleared by enhancing proteasome activity.