Isolated NC16a-ELISA testing is of little value to identify bullous pemphigoid in elderly patients with chronic pruritus

ARTICLE

Auteur(s) : Silke C Hofmann¹, Claudia Otto¹, Leena Bruckner-Tuderman¹, Luca Borradori²

¹Department of Dermatology, University Medical Center Freiburg, Hauptstrasse 7, D-79104 Freiburg, Germany
²Department of Dermatology, Inselspital, University of Berne, Switzerland

We read with interest the recent article of Jedlickova et al. on “Anti-basement membrane zone antibodies in elderly patients with pruritic disorders and diabetes mellitus” [1]. By indirect immunofluorescence (IF) microscopy using monkey oesophagus they were able to detect circulating antibodies against basement membrane zone (BMZ) proteins in up to 19% of 31 serum samples obtained from elderly patients with pruritic skin disorders, but without diabetes. Half of the latter also showed reactivity with recombinant forms of BP180 (collagen XVII) and/or BP230 by ELISA. In extension to this study, we here report our preliminary results of a follow-up study on the usefulness of the NC16a-ELISA in identifying elderly patients with pruritus who are potentially destined to develop bullous pemphigoid (BP). BP is the most common autoimmune subepidermal bullous dermatosis affecting predominantly the elderly, in which pruritus may be one of the leading initial symptoms of the disease [2]. Its diagnosis is usually based on combined clinical features, histological and immunopathological findings. The major antigenic target in BP is the NC16A-domain of BP180, recombinant forms of which have been used to establish ELISAs for rapid sensitive and specific diagnosis of BP as well as for monitoring disease activity in affected patients [3]. In this study, 15 patients aged ≥ 65 years (80.3 ± 10.7 years) with pruritus of at least 6-week-duration, and 34 age-matched controls without pruritus were assessed by NC16A-ELISA and indirect IF microscopy at the first visit and after 6 months. Most patients had dry skin and excoriations. Individuals with eczematous, urticarial or prurigo-like skin lesions, or with underlying infectious, metabolic or allergic disorders were excluded from the study. For ELISA, a prokaryotic GST-tagged NC16A-protein encompassing amino acids 490-567 of BP180 was used as described [4]. The cut-off value was determined as mean + 3 SD of 50 healthy individuals (OD 0.30). At first presentation, 4/15 (27%) patients with chronic pruritus displayed low-titer antibodies against the NC16A-domain (OD < 0.57). After 6 months, two of these patients still had persisting low-titer antibodies (OD 0.40), despite the disappearance of pruritus at that time (table 1). In the control group, 2/34 sera (6%) reacted slightly positively with the NC16a-domain (OD 0.31 and 0.44). None of the patients and control subjects showed positive indirect IF microscopy findings using human salt-split-skin as substrate and none developed BP during the observational period. Although the duration of pruritus varied from 6 weeks to 10 years, most patients were in clinical remission after 6 months of follow up, probably as a result of improved skin care with hydrating creams. Some patients had also been treated intermittently with non-sedating antihistaminics. Our study was motivated by previous findings demonstrating reactivity to the NC16a-domain of BP180 by ELISA in 3/25 (12%) sera from elderly patients with itch [5]. We wondered whether these patients suffered from an initial form of BP and therefore initiated this follow-up study. Considering the relatively low incidence of BP, even in the elderly [6], the number of prospectively followed patients in this study is insufficient to draw any conclusion about the predictive value of positive NC16A-ELISA results to identify elderly subjects who will develop BP. Although the NC16a-ELISA has been claimed to have a specificity of > 95% in the diagnosis of BP, the data reported here and previous data (summarized in table 2) clearly indicate that slightly positive NC16a-ELISA values or low-titer anti-BMZ-antibodies in general are frequently found in elderly patients with itch. The varying percentage of sera with circulating antibodies against basement membrane components (table 2) may depend on several factors including differences in patient selection and test systems. ELISA systems used in these studies are not directly comparable, since recombinant proteins were differentially expressed and represented various domains of BP180 or BP230.
Table 1 Characteristics of patients

In summary, isolated ELISA testing for BP antibodies is too expensive for little return in clinical practice [1, 5, 7, 8]. Therefore, diagnosis of BP should always be based on a combination of clinical features and positive direct IF microscopy studies.

Acknowledgments

References

2 Lamb PM, Abell E, Tharp M, et al. Prodromal bullous pemphigoid. Int J Dermatol 2006; 45: 209-14.

3 Schmidt E, Obe K, Brocker EB, et al. Serum levels of autoantibodies to BP180 correlate with disease activity in patients with bullous pemphigoid. Arch Dermatol 2000; 136: 174-8.

4 Di Zenzo G, Thoma-Uszynski S, Fontao L, et al. Multicenter prospective study of the humoral autoimmune response in bullous pemphigoid. Clin Immunol 2008; 128: 415-26.

5 Hofmann SC, Tamm K, Hertl M, et al. Diagnostic value of an enzyme-linked immunosorbent assay using BP180 recombinant proteins in elderly patients with pruritic skin disorders. Br J Dermatol 2003; 149: 910-2.

6 Alexandroff AB, Harman KE. Blistering skin disorders: an evidence-based update. Conference report. Br J Dermatol 2008.

7 Rieckhoff-Cantoni L, Bernard P, Didierjean L, et al. Frequency of bullous pemphigoid-like antibodies as detected by western immunoblot analysis in pruritic dermatoses. Arch Dermatol 1992; 128: 791-4.

8 Feliciani C, Caldarola G, Kneisel A, et al. IgG autoantibody reactivity against bullous pemphigoid (BP) 180 and BP230 in elderly patients with pruritic dermatoses. Br J Dermatol 2009 (in press: DOI 10.1111/j.1365-2133.2009.09266.x)