Current Perspectives on Erythema Multiforme.

Recognition and timely adequate treatment of erythema multiforme remain a major challenge. In this review, current diagnostic guidelines, potential pitfalls, and modern/novel treatment options are summarized with the aim to help clinicians with diagnostic and therapeutic decision-making. The diagnosis of erythema multiforme, that has an acute, self-limiting course, is based on its typical clinical picture of targetoid erythematous lesions with predominant acral localization as well as histological findings. Clinically, erythema multiforme can be differentiated into isolated cutaneous and combined mucocutaneous forms. Atypical erythema multiforme manifestations include lichenoid or granulomatous lesions as well as lesional infiltrates of T cell lymphoma and histiocytes. Herpes simplex virus infection being the most common cause, other infectious agents like-especially in children-Mycoplasma pneumoniae, hepatitis C virus, Coxsackie virus, and Epstein Barr virus may also trigger erythema multiforme. The second most frequently identified cause of erythema multiforme is drugs. In different studies, e.g., allopurinol, phenobarbital, phenytoin, valproic acid, antibacterial sulfonamides, penicillins, erythromycin, nitrofurantoin, tetracyclines, chlormezanone, acetylsalicylic acid, statins, as well as different TNF-α inhibitors such as adalimumab, infliximab, and etanercept were reported as possible implicated drugs. Recently, cases of erythema multiforme associated with vaccination, immunotherapy for melanoma, and even with topical drugs like imiquimod have been described. In patients with recurrent herpes simplex virus-associated erythema multiforme, the topical prophylactic treatment with acyclovir does not seem to prevent further episodes of erythema multiforme. In case of resistance to one virostatic drug, the switch to an alternative drug, and in patients non-responsive to virostatic agents, the use of dapsone as well as new treatment options, e.g., JAK-inhibitors or apremilast, might be considered.

Current Perspectives on Stevens-Johnson Syndrome and Toxic Epidermal Necrolysis.

Stevens-Johnson syndrome (SJS) and toxic epidermal necrolysis (TEN) are considered a delayed-type hypersensitivity reaction to drugs. They represent true medical emergencies and an early recognition and appropriate management is decisive for the survival. SJS/TEN manifest with an "influenza-like" prodromal phase (malaise, fever), followed by painful cutaneous and mucous membrane (ocular, oral, and genital) lesions, and other systemic symptoms. The difference between SJS, SJS/TEN overlap, and TEN is defined by the degree of skin detachment: SJS is defined as skin involvement of < 10%, TEN is defined as skin involvement of > 30%, and SJS/TEN overlap as 10-30% skin involvement. The diagnosis of different degrees of epidermal necrolysis is based on the clinical assessment in conjunction with the corresponding histopathology. The mortality rates for SJS and TEN have decreased in the last decades. Today, the severity-of-illness score for toxic epidermal necrolysis (SCORTEN) is available for SJS/TEN severity assessment. Drugs with a high risk of causing SJS/TEN are anti-infective sulfonamides, anti-epileptic drugs, non-steroidal anti-inflammatory drugs of the oxicam type, allopurinol, nevirapine, and chlormezanone. Besides conventional drugs, herbal remedies and new biologicals should be considered as causative agents. The increased risk of hypersensitivity reactions to certain drugs may be linked to specific HLA antigens. Our understanding of the pathogenesis of SJS/TEN has improved: drug-specific T cell-mediated cytotoxicity, genetic linkage with HLA- and non-HLA-genes, TCR restriction, and cytotoxicity mechanisms were clarified. However, many factors contributing to epidermal necrolysis still have to be identified, especially in virus-induced and autoimmune forms of epidermal necrolysis not related to drugs. In SJS/TEN, the most common complications are ocular, cutaneous, or renal. Nasopharyngeal, esophageal, and genital mucosal involvement with blisters, erosions as well as secondary development of strictures also play a role. However, in the acute phase, septicemia is a leading cause of morbidity and fatality. Pulmonary and hepatic involvement is frequent. The acute management of SJS/TEN requires a multidisciplinary approach. Immediate withdrawal of potentially causative drugs is mandatory. Prompt referral to an appropriate medical center for specific supportive treatment is of utmost importance. The most frequently used treatments for SJS/TEN are systemic corticosteroids, immunoglobulins, and cyclosporine A.

Drug-induced angioedema.

Angioedema (AE) is the end result of deep dermal, subcutaneous and/or submucosal swelling, and represents a major criterion in the definition of anaphylaxis. Drug-induced AE, like other cutaneous drug reactions, is most frequently elicited by betalactam antibiotics and nonsteroidal antiinflammatory drugs. However, differences exist in their underlying pathophysiology (IgE mediated vs. pseudoallergic). Blockers of the renin-angiotensin-aldosterone system are the most common class of medications associated with isolated AE and are most probably related to elevated bradykinin levels. Typically, ACE inhibitor-associated AE can occur up to several years after initiating treatment, and may sporadically recur even after discontinuation. A comprehensive investigation of AE must include analysis of complement factors, tryptase levels as well as specific allergy tests. Furthermore, other possible causative agents ought to be excluded. Every patient with drug-induced AE must receive an allergy pass as well as emergency medication including epinephrine. In some cases, inhibitors of the bradykinin system may be considered for treatment.

Cross-reactivity patterns of T cells specific for iodinated contrast media.

BACKGROUND: Approximately 3% of patients exposed to iodinated contrast media develop delayed hypersensitivity reactions. OBJECTIVE: We wanted to better understand the molecular basis of contrast media cross-reactivity. METHODS: Cross-reactivity was assessed by skin testing and measurement of T-cell activation (CD69 upregulation) and proliferation ((3)H-thymidine uptake, 5,6-carboxyfluorescein diacetate succinimidyl ester staining) of PBMCs, T-cell lines, and T-cell clones of 2 patients with delayed hypersensitivity reactions to iohexol and iomeprol, respectively. Thirteen different contrast media and potassium iodide were compared. RESULTS: Skin testing and analyses of PBMCs, T-cell lines, and clones showed broad cross-reactivity in both patients. Broad as well as more restricted cross-reactivity patterns were found in iohexol-specific and iomeprol-specific CD4(+) T-cell clones, whereas 1 iomeprol-specific CD8(+) T-cell clone showed no cross-reactivity at all. The reactivity to equimolar concentrations of iohexol and its dimer iodixanol was very similar, suggesting that the dimer was not more stimulatory than its monomer. Consistently low reactivity to iobitridol was found in both patients, but never to iodide. A frequency analysis of contrast medium-specific peripheral T cells gave values between 0.6 % (iomeprol) and 0.05 % (iobitridol). CONCLUSION: Clinically observed cross-reactivity between different contrast media is a result of the presence of contrast media-specific T cells, some of which show a broad cross-reactivity pattern. Iodide ions, known to be present at low concentration in contrast media solutions, do not seem to be the causative moiety. CLINICAL IMPLICATIONS: Detailed in vitro analysis might help identify noncross-reactive contrast media.

Pharmacological interaction of drugs with immune receptors: the p-i concept.

Drug-induced hypersensitivity reactions have been explained by the hapten concept, according to which a small chemical compound is too small to be recognized by the immune system. Only after covalently binding to an endogenous protein the immune system reacts to this so called hapten-carrier complex, as the larger molecule (protein) is modified, and thus immunogenic for B and T cells. Consequently, a B and T cell immune response might develop to the drug with very heterogeneous clinical manifestations. In recent years, however, evidence has become stronger that not all drugs need to bind covalently to the MHC-peptide complex in order to trigger an immune response. Rather, some drugs may bind directly and reversibly to immune receptors like the major histocompatibility complex (MHC) or the T cell receptor (TCR), thereby stimulating the cells similar to a pharmacological activation of other receptors. This concept has been termed pharmacological interaction with immune receptors the (p-i) concept. While the exact mechanism is still a matter of debate, non-covalent drug presentation clearly leads to the activation of drug-specific T cells as documented for various drugs (lidocaine, sulfamethoxazole (SMX), lamotrigine, carbamazepine, p-phenylendiamine, etc.). In some patients with drug hypersensitivity, such a response may occur within hours even upon the first exposure to the drug. Thus, the reaction to the drug may not be due to a classical, primary response, but rather be mediated by stimulating existing, pre-activated, peptide-specific T cells that are cross specific for the drug. In this way, certain drugs may circumvent the checkpoints for immune activation imposed by the classical antigen processing and presentation mechanisms, which may help to explain the peculiar nature of many drug hypersensitivity reactions.

The immunological and clinical spectrum of delayed drug-induced exanthems.

PURPOSE OF REVIEW: Drug-induced exanthems are the most common manifestations of drug hypersensitivity and are observed in as much as 2-3% of hospitalized patients. Here we summarize new concepts of the immune mechanisms underlying various forms of drug-induced exanthems. RECENT FINDINGS: Alpha-betaTCR+, CD4 and CD8+ T cells are involved in different drug hypersensitivity reactions. Their function determines the clinical picture. In maculopapular, bullous and pustular exanthems cytotoxic T cells are involved, while a high IL-5 and eotaxin production by tissue cells is frequently found in maculopapular and occasionally in bullous and in pustular exanthems. High IL-8 (CXCL-8) and granulocyte-macrophage colony stimulating factor production by T cells is a hallmark of pustular drug exanthems. In the most severe and potentially life-threatening forms of exanthems (Stevens-Johnson syndrome/toxic epidermal necrolysis) cytotoxic CD8+ T cells with natural killer cell markers can be found in the blister fluid. SUMMARY: These findings are the basis for a new subclassification of delayed, type IV hypersensitivity reactions into type IVa (T helper type 1 cells, e.g. tuberculin reaction and contact dermatitis), IVb (T helper type 2 cells, maculopapular exanthem with eosinophilia), IVc (cytotoxic T cells, contact dermatitis, maculopapular and bullous exanthem), and IVd reactions (CXCL-8/granulocyte-macrophage colony stimulating factor-producing T cells and neutrophil attraction, pustular exanthems), by which, in most reactions, various mechanisms occur together but one reaction dominates the clinical picture.

Systemically induced allergic exanthem from mercury.

Cutaneous reactions to mercury can manifest themselves in different forms. Apart from contact dermatitis, flare-up reactions, disseminated exanthem as well as skin symptoms in previously unaffected skin are known. Regarding systemic allergen application, 2 separate clinical patterns, namely acute generalized exanthematous pustulosis (AGEP) and symmetric flexural exanthem 'baboon syndrome' have been described. Systemic allergic reactions to mercury are most commonly provoked by the inhalation of metallic mercury vapours from a broken thermometer, often after previous sensitization to mercury compounds, e.g. Mercurochrome. Patch testing with mercurials yields positive reactions in approximately 80% of patients. We report 3 patients, 2 with flexural exanthem, and 1 presenting with AGEP, respectively. Positive patch tests to mercury derivatives could be demonstrated in all of them. Furthermore, non-toxic serum mercury levels were detected in 2 of the patients. The present review provides a survey of the literature on systemic allergic exanthem to mercury. However, plausible explanations for the distribution pattern of the skin manifestations in AGEP and flexural exanthem are still lacking.