Meta-analysis of the clinical and immunopathological characteristics and treatment outcomes in epidermolysis bullosa acquisita patients

Epidermolysis bullosa acquisita (EBA) was first used as a descriptive diagnostic term for the adult onset of a disease resembling epidermolysis bullosa dystrophica at the beginning of the twentieth century [1]. In 1971, Roenigk et al. established the first diagnostic criteria for EBA. An EBA diagnosis depends on the following criteria: (i) clinical lesions resembling epidermolysis bullosa dystrophica; (ii) adult onset of disease; (iii) a negative family history of epidermolysis bullosa dystrophica; and (iv) exclusion of other bullous diseases [2]. In 1973, Kushniruk first noted the deposition of IgG and C3 along the dermal-epidermal junction in EBA patients [3]. These immune deposits were located beneath the lamina densa in the anchoring fibril zone as determined by immunoelectron microscopy (IEM); clearly in a different localization than immune deposits observed in patients with bullous pemphigoid [4, 5]. Subsequently, a putative 290 kD autoantigen located at the skin basement-membrane was identified [6] and later recognized as type VII collagen (COL7), the major component of anchoring fibrils at the dermal-epidermal junction [7]. The pathogenicity of autoantibodies targeting COL7 has been independently demonstrated both in vitro, ex vivo and in vivo [8‐11]. Hence, EBA is classified as an organ-specific autoimmune disease. Based on this understanding, the detection of tissue-bound antibodies at the basement membrane zone in specimens from peri-lesional skin or mucous membrane biopsies and autoantibodies specific to COL7 is the current standard for EBA diagnosis [12‐14]. Previously direct IEM was the gold standard for a definite EBA diagnosis. It is still an alternative in seronegative EBA. Based on the specific COL7 expression pattern, EBA can also be diagnosed via detection of a u-serrated pattern by direct IF microscopy [15] or Fluorescent Overlay Antigen Mapping (FOAM) [16].

The clinical presentation of EBA is diverse. In the mechano-bullous (MB, non-inflammatory, classical) disease variant, patients suffer from skin fragility, tense blisters, scarring and milia formation primarily localized to trauma-prone sites and the extensor skin surface. In these patients, nail dystrophy, post-inflammatory hyper- and hypopigmentation are also frequently observed. In mild cases, the clinical presentation is similar to porphyria cutanea tarda, whereas severe cases are comparable to hereditary recessive dystrophic epidermolysis bullosa. EBA can also resemble other autoimmune bullous dermatoses (AIBD), such as bullous pemphigoid (BP), linear IgA disease (LAD), mucous membrane pemphigoid (MMP) or Brunsting–Perry pemphigoid. In these patients, widespread vesiculobullous eruptions are observed, typically involving the trunk, central body, extremities and skin folds. The patients typically suffer from pruritus. These variants are categorized as non-MB EBA [14, 17‐21]. An individual patient may present with either one of these variants alone or in combination. In addition, a patient’s clinical presentation may change from one variant to the other during the disease course [8]. However, data on the prevalence of the different phenotypes of EBA are not available.

Given that COL7 is expressed in the gastro-intestinal tract, the involvement of the oral cavity and other mucosal sites has been frequently reported – and thus EBA must be considered a mucocutaneous disease [14, 20, 22‐24]. In addition, other mucous membrane involvement, e.g. ocular and genital, have been repetitively noted in EBA patients, and extracutaneous involvement may occur more often than currently recognized given that a detailed evaluation of mucosal involvement by a multidisciplinary team of medical care providers indicated extensive mucosal involvement [25, 26]. Again, a comprehensive overview on mucosal involvement and affected organs is not available.

In addition to concomitant mucosal involvement, EBA has also been reported to be associated with cancer as well as inflammatory, infectious, cardiovascular, metabolic and neurological diseases [21, 27‐33]. However, most of these findings are case reports, and no clear pathogenetic interaction between EBA and these diseases has been established. By contrast, accumulating evidence suggests an association between EBA and inflammatory bowel diseases (IBDs), such as ulcerative colitis (UC) and Crohn’s disease (CD). IBD is reported to be present in approximately 30% of EBA patients. CD is associated with EBA in at least 25 cases [23, 34, 35] and four EBA cases have been reported to be associated with UC [35]. In EBA patients with CD, circulating COL7 antibodies have been noted in frequencies ranging from 6 to 60% [23, 36, 37]. However, these findings must be interpreted with caution as many of these observations were made before the modern diagnostic criteria for EBA were established [38‐40]. Further evidence of a pathogenic link between IBD and EBA was obtained from EBA mouse models. In both antibody transfer-induced and immunization-induced EBA, blister formation was observed in the esophagus, stomach, small intestine, and colon in addition to the skin [24]. The prevalence of blister formation in these mouse models parallels COL7 expression, which decreases from proximal to distal regions of the gastrointestinal tract. This anti-COL7-induced gastrointestinal tissue injury is functionally relevant as weight loss or failure to gain weight appropriately gain weight was noted in diseased mice [24].

Despite several in depth reviews on EBA [41‐43], detailed insights into the epidemiological, clinical and immunological characteristics of EBA patients on a larger scale are not available. However, this information would be valuable for coordinating standardized diagnostic and therapeutic interventions as well as planning future clinical trials. Therefore, we collected these data from all EBA cases published from 1971 to 2016 that fulfilled the current diagnostic criteria.

Our meta-analysis documents the clinical and immunopathological characteristics from EBA patients published between 1971 and 2016. The evaluation of treatment outcomes provides insights on the efficacy of current EBA treatments.

From a literature search to establish our meta-analysis cohort, we found several EBA case reports in which the diagnosis could not be validated based on our pre-defined inclusion criteria. When EBA is clinically considered as a potential differential diagnosis, it should only be diagnosed if in addition to linear Ig deposits via direct IF microscopy of a skin biopsy or immunoelectron microscopy findings of EBA and fulfill any of the following criteria: (i) detection of anti-COL7 antibodies (any method) or a 290 kD band via western blotting of dermal extracts [44]; (ii) detection of a u-serrated pattern in direct IF microscopy [15]; (iii) FOAM; or (iv) split mapping techniques [4, 16, 45]. When determining the exact diagnosis of EBA, the inclusion of defined criteria for its subtypes is crucial for planning and conducting interventional clinical trials; moreover, an international consensus and standard should be established. Yet, these selection criteria may have led to non-inclusion of “true” EBA cases into the analysis. For example, cases reported with typical clinical features, linear IgG deposits in direct IF microcopy and dermal binding of patient IgG to the dermal side of salt spit skin [57, 58]. Furthermore, differentiation of EBA from LAD with anti-COL7 IgA autoantibodies [59] or “MMP” patients with autoimmunity to COL7 may differ among institutions. Herein, we applied the recently established diagnostic criteria for EBA [14, 59] to differentiate between these diseases.

With the exception of a trend towards the detection of IgA deposits by direct IF microscopy in non-MB EBA but not in MB EBA [17], no laboratory parameter has been reported to be able to distinguish between these EBA variants [8]. In the cohort evaluated in this meta-analysis, IgA deposits, as well as IgG, IgM and C3 deposits, were also more frequently observed in non-MB EBA (Table 2). Furthermore, additional laboratory parameters analyzed in this study could not be used to distinguish between these EBA variants. In addition, IgA deposits were also observed more frequently in MM EBA as opposed to EBA patient without MM involvement. Here, we documented a high prevalence of mucous membrane involvement in EBA, which confirms findings from a previous investigation of four EBA patients [25]. We also believe that inclusion of duplicate cases (i.e. in serological studies) may have “diluted” the prevalence of mucous membrane involvement in our analysis, and that the frequency of this complication is more frequent. Therefore, EBA patients should be monitored for mucous membrane involvement at regular intervals.

Based on the prevalence of autoimmune and chronic inflammatory diseases associated with EBA [60], the observed occurrence of EBA with CD, UC, and other AIBD appears to be higher than expected, whereas other reported EBA-associated diseases seem to occur at rates that are similar to those in the general population. Of note, the here-observed frequency of CD and UC association with EBA is much lower to previous reports, where CD/UC IBD has been reported to be present in approximately 30% of patients with EBA. But some of these observations were made before modern diagnostic criteria for EBA had been established [24]. Hence, the association of EBA with CD and UC seems likely, but needs to be determined prospectively. Interestingly, ANAs were detected in 20.0% of EBA patients, whereas ANA prevalence in healthy controls ranges between 8 and 24% [61‐65]. Thus, ANA reactivity seems increased in EBA patients. This observation may indicate that EBA, like pemphigus [66], shares early pathogenic events systemic with systemic lupus erythematous. This notion is strengthened by the clinical disease entity of bullous lupus erythematous [17], an autoantibody-mediated (mostly anti-COL7) subepidermal blistering disease that occurs in patients with systemic erythematosus. Again, as stated above, the methodology used herein most likely underestimates the comorbidity in EBA patients.

Most importantly, our meta-analysis detected significant differences regarding the efficacy of current EBA treatments. First, we document significant variations in EBA treatments, confirming a previous report [67]. Despite the limitations of our analysis, i.e., retrospective nature of the study, inhomogeneity, exclusion of potentially “true” EBA cases (see above) with reported treatment outcomes from the analysis (especially those relating to cyclosporine), and publication bias from the case report primary data, this meta-analysis provides insights into therapeutic efficacy in a large collection of EBA patients. Based on the results from our meta-analysis, which only computed associations of single treatments with the induction of clinical remission, independent of any possible combinatory treatments, IVIG and rituximab seem likely candidates to be used in combination therapies as a treatment for EBA patients. Other associations of treatment efficacy are based on too few cases to draw further conclusions; i.e. 6 cases treated with extracorporeal photopheresis (ECP, Additional file 1: Table S1). This information, as mentioned above, has to be interpreted with caution, but may be useful to guide the planning of clinical trials in EBA patients. To establish the rationale for a controlled clinical trial in EBA patients, the therapeutic efficacy of “established” and emerging EBA treatments should be evaluated in parallel using animal models of the disease [10, 11, 68]. Use of these models has identified several compounds with therapeutic efficacy, including IVIG, as well as potential therapeutic targets [69‐71]. The results from coordinated observational studies and therapeutic interventions in animal models will hopefully serve as a basis for the design of a controlled clinical trial in EBA patients. Yet, again, the strict inclusion criteria may have led to non-inclusion of treated EBA patients, which may have had an impact on the analysis.

In summary, based on the meta-analysis of case reports and case report series, we provide insights into the clinical and immunopathological characteristics and treatment outcomes in all published EBA cases from 1971 to 2016. In addition, this study seeks to improve our understanding of EBA pathogenesis and the limited treatment options. There is a great need to establish an international EBA patient registry, including a collection of prospectively collected biomaterials to foster our further understanding of this disease.