A retrospective analysis of tissue-fixed immunoreactants from skin biopsies maintained in Michel's medium

Diagnostic utility of direct immunofluorescence test panels for cutaneous vasculitis: A scoping review

BACKGROUND

Due to the immune-mediated nature of non-infectious cutaneous vasculitis, skin biopsy specimens are often submitted for direct immunofluorescence (DIF) testing when vasculitis is considered clinically. However, evidence regarding the clinical value of DIF has not been rigorously appraised.

OBJECTIVE

In this scoping review, we aimed to systematically evaluate the peer-reviewed literature on the utility of DIF in vasculitis to assist with the development of appropriate use criteria by the American Society of Dermatopathology.

METHODS

Two electronic databases were searched for articles on DIF and vasculitis (January 1975-October 2023). Relevant case series involving more than or equal to three patients, published in English, and with full-text availability were included. Additional articles were identified manually via reference review. Due to study heterogeneity, findings were analyzed descriptively.

RESULTS

Of 255 articles identified, 61 met the inclusion criteria. Cumulatively representing over 1000 DIF specimens, several studies estimated DIF sensitivity to be 75%. While vascular immunoglobulin A (IgA) deposits on DIF were associated with renal disease, other systemic associations were inconsistent. Vascular IgG deposition may be overrepresented in ANCA-associated vasculitis. Granular vascular and epidermal basement membrane zone Ig deposition differentiated hypocomplementemic from normocomplementemic urticarial vasculitis. Few studies have assessed the added value of DIF over routine microscopy alone in vasculitis.

CONCLUSIONS

This scoping review discovered that DIF testing for vasculitis has been performed not only for diagnostic confirmation of vasculitis but also for disease subtype classification and prediction of systemic associations. Future studies on test sensitivity of DIF compared to that of histopathology are needed.

Diagnostic Techniques in Autoimmune Blistering Diseases

Autoimmune blistering diseases (AIBD) comprise a heterogeneous group of uncommon disorders of the skin and mucous membranes, characterised by antibodies targeting structural proteins within epithelial tissue and the underlying basement membrane. There can be significant overlap in clinical presentation of these diseases and accurate diagnosis relies on the detection and characterisation of relevant autoantibodies. Immunofluorescence provides the gold-standard diagnostic tool for these diseases, identifying both tissue-bound autoantibodies in biopsy material using direct immunofluorescence and circulating antibodies in serum through indirect immunofluorescence. Following advances in the identification and subsequent characterisation of numerous antigenic targets in these diseases, the development of antigen-specific tests, in particular, enzyme-linked immunosorbent assays on serum specimens, has provided a third key tool to not only identify, but also quantify AIBD autoantibodies. This quantification has proven particularly useful in monitoring disease activity and informing clinical management decisions. Accurate diagnosis of these diseases is important since optimal treatment strategies differ between them and, prognostically, some diagnoses are associated with an increased risk of malignancy. This review outlines the molecular pathology underlying the major AIBD and describes how the three principal techniques can be used in combination, to provide best practice for diagnosis and treatment monitoring.

Practical Direct Immunofluorescence

Direct immunofluorescence (DIF) remains a valuable tool that may be underused because of perceived challenges in the interpretation, limitations, and processing of DIF specimens. The aim of this review is to provide a practical guide for appropriately incorporating DIF in a variety of clinical diseases, such as autoimmune blistering disorders. In vasculitis, the role of DIF continues to evolve, particularly in the setting of IgA vasculitis. Although typically not indicated for the workup of connective tissue disease, DIF may be helpful in cases with negative serologies, nondiagnostic histologic findings, or scarring alopecia. Practical pearls for biopsy technique, specimen handling, and storage are also discussed.

Advances in the diagnosis of autoimmune bullous dermatoses

Autoimmune bullous dermatoses are defined by autoantibodies directed against adhesion proteins in the epidermis or basement membrane zone, resulting in blister formation on the skin and mucosa. Diagnosis depends on lesional biopsy for histopathology and perilesional biopsy for direct immunofluorescence. Additional diagnostic methods include indirect immunofluorescence, enzyme-linked immunosorbent assay, and immunoblot (Western blot), which may be selected in specific clinical scenarios due to improved sensitivity and/or specificity. This contribution reviews the available evidence supporting the use of each method to provide a practical reference for clinicians when diagnosing autoimmune bullous disorders. Techniques and cost are reviewed, and newer diagnostic techniques with potential for clinical application are.

A comparative study of Michel's medium versus honey as a transport medium for skin specimens prior to direct immunofluorescence microscopy and antigen mapping

BACKGROUND

Michel's medium (MM) is currently the recommended transport medium for skin biopsy specimens prior to direct immunofluorescence (DIF) microscopy.

OBJECTIVE

To compare the utility of honey with that of MM as a transport medium for skin biopsy specimens used for DIF and antigen mapping.

METHODS

Group I consisted of 45 freshly-taken skin specimens earmarked for DIF testing. It was divided into three groups (A, B and C), each containing 15 specimens. Biopsy specimens were sliced into two, one each for MM and honey. Samples in group A were processed at the end of week 1 while those in group B and C were processed at the end of weeks 2 and 4, respectively. Group II consisted of five specimens of epidermolysis bullosa (EB) which was further divided into three groups; two specimens were processed for antigen mapping at the end of week 1, while others were processed at the end of week 2 (two specimens) and 4 (one specimen).

RESULTS

Sensitivity of honey as a transport medium for skin biopsy specimens was 100%, 92.6% and 53.8% at weeks 1, 2 and 4, respectively. The antigen mapping was positive in all specimens.

CONCLUSION

Utility of honey was comparable to MM for DIF samples tested at weeks 1 and 2 but was lower at week 4.

Dermatologic Urgencies and Emergencies: What Every Pathologist Should Know

CONTEXT.—

Fatal dermatologic diseases and ones with high morbidity can occur in the inpatient setting. In such cases, prompt and accurate assessment of a bedside skin biopsy is required. This may be challenging for many pathologists who are not familiar with the complexity of skin pathology and skin terminology within the fields of dermatopathology and dermatology.

OBJECTIVE.—

To provide the pathologist with a practical, up-to-date, and "must-know" reference guide on dermatologic urgencies and emergencies from a real-world perspective, highlighting diagnostic pearls, diagnostic pitfalls, and commonly encountered practice gaps. This review will focus on key diseases with which every pathologist should be familiar, including angioinvasive fungal infections, Stevens-Johnson syndrome/toxic epidermal necrolysis, staph-scalded-skin syndrome, acute graft-versus-host disease, bullous pemphigoid, calciphylaxis, Sweet syndrome and its histiocytoid variant, pyoderma gangrenosum, and leukocytoclastic vasculitis, as well as those in their clinical and histopathologic differential.

DATA SOURCES.—

This review is based on peer-reviewed literature and our personal experiences with these diseases at major academic institutions, including one where a large number of stem cell transplants are performed. This review is unique as it represents collaborative expert opinion from both a dermatopathology and a dermatology standpoint.

CONCLUSIONS.—

This review outlines the critical role that the pathologist plays in the outcomes of patients with dermatologic urgencies and emergencies. Improved patient care will result from prompt and accurate histopathologic diagnoses as well as an open line of communication with the dermatologist.

Utility of immunofluorescence in dermatology

Immunofluorescence (IF) tests have redefined our understanding of many immune-mediated skin diseases, especially autoimmune blistering diseases (AIBDs). Nomenclature of certain AIBDs (for example, linear IgA diseases and IgA pemphigus) has been done based solely on the finding of tissue-bound immunoreactants as detected by IF tests. Direct and indirect are the two major types of IF tests; they are not only useful in the diagnosis but also guide the clinician in the treatment at least in certain AIBDs, as the titer of circulating antibodies as detected by IF reflects the disease activity. In this review, we describe techniques, various types of IF, and its modification.

Michel's Transport Medium as an Alternative to Liquid Nitrogen for PCR Analysis of Skin Biopsy Specimens

Formalin fixation and paraffin embedding are standard procedures for histopathological diagnosis and allow long-term archiving of tissue specimens. The cross-linking properties of formalin cause fragmentation of nucleic acids and reduce the sensitivity of PCR analysis. Michel's medium is a well-established transport medium used by dermatologists for biopsy transport to maintain tissue-fixed immunoreactants prior to direct immunofluorescence and immunoelectron microscopy. Here we report that Michel's medium also allows short-term preservation of DNA for PCR analysis and permits amplification of amplicons larger than 1 kb. Therefore, Michel's medium appears to be a reserve medium for performing PCR when no other samples are available.

Métodos diagnósticos en las enfermedades ampollosas subepidérmicas autoinmunes

There is considerable clinical and histological overlap among the subepidermal autoimmune bullous diseases. The knowledge at the molecular level of the dermo-epidermal junction is essential to understand this group of diseases. The immune-based techniques have contributed to increase the knowledge of these entities and have been progressively incorporated into clinical practice. In this review of the diagnostic methods of subepidermal autoimmune bullous diseases we summarize the most recent advances on the molecular biology of the dermo-epidermal junction, focusing on the immune-based diagnostic techniques. We distinguish two main groups of diagnostic methods: those that detect autoimmune deposits in the skin (direct immunofluorescence and its variants including confocal microscopy) and those that detect antibodies in serum or in other fluids (indirect immunofluorescence and its variants, ELISA, immunoblot and immunoprecipitation). We explain the methodology and diagnostic keys of the techniques most widely applied in our milieu.

Enhanced diagnostic immunofluorescence using biopsies transported in saline

Background

The demonstration of tissue-bound immunoreactants by direct immunofluorescence microscopy (DIF) is a valuable parameter in the diagnosis of various autoimmune and immunecomplex-mediated skin diseases. For preservation of tissue-bound immunoreactants, biopsies are usually fresh-frozen in liquid nitrogen or transported in Michel's fixative. But even optimally preserved tissue specimens are no guarantee for the correct diagnosis by DIF, especially when weak to moderate IgG fluorescence of the epidermal basement membrane zone is involved. In such cases false negative results are easily obtained due to the relatively high dermal "background" fluorescence produced by polyclonal anti-human IgG fluorescein conjugates.

Methods

In the present study we have compared the use of normal saline (0.9% NaCl) with liquid nitrogen and Michel's fixative as transport medium for skin biopsies. From 25 patients with an autoimmune skin disease (pemphigus, pemphigoid, lupus erythematosus and vasculitis) four matched skin biopsies were obtained and transported in either saline for 24 and 48 hours, liquid nitrogen, or Michel's fixative for 48 hours.

Results

Direct IF microscopy showed significant reduction of background fluorescence (p < 0.01) and relatively enhanced desired specific (IgG, IgA) staining in biopsies transported in saline. A conclusive or tentative IF diagnosis was reached in 92% after 24 h saline, 83% after 48 h saline, 68% after freezing in liquid nitrogen, and 62% after 48 h Michel's medium (n = 25).

Conclusions

We conclude that transporting biopsies without freezing in normal saline for 24 hours is an adequate and attractive method for routine IF diagnosis in autoimmune and immune complex-mediated dermatoses. The superior results with saline incubation are explained by washing away of IgG background in dermis and epidermis.

The use of Michel's transport medium for immunofluorescence and immunoelectron microscopy in autoimmune bullous diseases

We report the use of Michel's solution, already a well established transport medium, in the combined use of direct immunofluorescence (IMF) and pre-embedding immunoelectron microscopy in 3 subepidermal bullous diseases--bullous pemphigoid (BP), epidermolysis bullosa acquisita (EBA) and dermal binding linear IgA disease (LABD). Our studies demonstrated that electron microscopy of normal skin maintained in Michel's medium for up to 28 days showed remarkable preservation of all components of the basement membrane zone, including the ultrastructure of the basal keratinocytes, dermoepidermal junction and papillary dermis. However, epidermal cell cytolysis occurred after just 48 hours. Immunoelectron microscopy using a gold probe has enabled us to localise the immunoreactants in bullous pemphigoid, epidermolysis bullosa acquisita and dermal-binding linear IgA bullous dermatoses. Our findings are comparable to and as equally reliable as those on immunoelectron microscopy of fresh skin biopsies with no loss of antigen deposition, and demonstrate an effective new use of a well established transport medium.