When Baker and Ryan described a series of 104 cases of pustular psoriasis in 19681 they detected a subgroup of 5 patients who had no history of psoriasis and in which the episode of pustular eruption was very acute, resolved quickly and did not recur. This group was named exanthematic pustular psoriasis and already then the authors suspected drugs and/or infections as trigger for the pustular skin reaction. In the meantime many cases with similar clinical features were described under different denominations such as toxic pustuloderma2 and pustular drug rash,3 or were interpreted as special variants of other pustular diseases. In 1980 Beylot et al.4 introduced the term pustuloses exanthématique aiguës généralisés (PEAG) to the French literature and it’s translation acute generalized exanthematous pustulosis (AGEP) is now broadly used in cases of pustular eruptions showing the clinical features discussed below. We will use the term AGEP throughout this paper well aware, that many reported cases of toxic pustuloderma are dealing with the same disease. A clear distinction has to be made from the term pustulosis acuta generalisata, which describes a poststreptococcal disease arising mainly in children and different from AGEP.5
Background: A wide range of diseases or reactions can cause pustular eruptions of the skin. In this spectrum there seems to be a subgroup with characteristic clinical features and a typical course which is mostly caused by drugs for which the term acute generalized exanthematous pustulosis (AGEP) has been established.
Objective: To describe the clinical features of AGEP.
Methods: The authors’ experience from a multinational epidemiological study on severe cutaneous adverse reactions and a comprehensive review of the literature were used to provide an overview of the disease and it’s possible causes. An algorithm for validating cases which was established for this study is also presented.
Results: AGEP typically presents with at least dozens of non follicular sterile pustules occurring on a diffuse, edematous erythema predominalty in the folds and/or on the face. Fever and elevated blood neutrophils are common. Histopathology typically shows spongiform subcorneal and/or intraepidermal pustules, a marked edema of the papillary dermis, and eventually vasculitis, eosinophils and/or focal necrosis of keratinocytes. Onset is acute, most often following drug intake, but viral infections can also trigger the disease. Pustules resolve spontaneously in less than 15 days.
Conclusion: The diagnosis AGEP should be considered in cases of acute pustular rashes and detection of the causative drug should be strived for. Knowledge of the clinical features and usual course of this disease can often prevent unnecessary therapeutical measures.
Clinical features, course, and laboratory findings
Mostly beginning in the intertriginous areas or in the face a diffuse, often edematous erythema develops very acutely. Patients often describe a burning or itching sensation. On this – often widespread – erythema soon dozens to hundreds of small (pinhead sized, <5 mm) non follicular sterile pustules arise mainly in the folds (Fig. 1). Sometimes confluence of pustules may mimic a positive Nikolsky’s sign and thus lead to a misinterpretation as toxic epidermal necrolysis (TEN). Other skin symptoms like marked edema of the face, purpura lesions (especially on the legs), Stevens-Johnson-syndrome-like “atypical targets”, blisters and vesicles have been described but are not typical for AGEP. Mucous membrane involvement may occur in about 20% of the cases but usually is mild and remains limited to one location (mostly oral).
Skin symptoms are almost always accompanied by fever above 38° Celsius and leucocytosis mostly due to blood neutrophil counts above 7×109/l. A mild eosinophilia may be present in about one third of the patients.6 Lymphadenopathy has been reported in some cases.7 Apart from a slight reduction of the creatinine clearance (<60 ml/min in ∼30% of the cases) and a mild elevation of aminotransferases, no involvement of other internal organs has to be expected.
The combination of high fever, leucocytosis and pustules is often misinterpreted as acute infectious disease. Early diagnosis of AGEP is important to avoid unnecessary investigations and/or the administration of expensive and sometimes risky antibiotics.
Pustules resolve spontaneously within a few (∼4 to 10) days and are – in typical cases – followed by a characteristic postpustular pin-point desquamation (Fig. 2). The overall prognosis is good in AGEP although high fever or superinfection of skin lesions can sometimes lead to life-threatening situations in patients of old age or poor general condition.
The typical histopathology of AGEP shows spongiform subcorneal and/or intraepidermal pustules, an often marked edema of the papillary dermis and perivascular infiltrates with neutrophils and exocytosis of some eosinophils.8 Vasculitis and/or some single cell necroses of keratinocytes may be present. Psoriatic changes like acanthosis and papillomatosis are usually absent.9
A wide spectrum of cutaneous diseases or reactions can cause pustular eruptions. Most of them can easily be differentiated from AGEP: all follicular eruptions like bacterial folliculitis, furunculosis, acne and acneiform pustules, localized pustular contact dermatitis, dermatophyte infections, pyoderma vegetans, varicella, Kaposi’s varicelliform eruption, Sweet’s syndrome, impetigo, impetiginized eczema, pemphigus foliaceus and other autoimmune bullous disorders, infantile chronic acropustulosis, migratory necrolytic eruption of glucagonoma, bowel bypass syndrome, Behcet’s disease or staphylococcal scalded skin syndrome and others. Yet a couple of diseases remain where differentiation from AGEP may cause problems both, clinically and conceptually.
Pustular psoriasis (von Zumbusch type)
One of the main issues in the discussion whether AGEP (or toxic pustuloderma) is an entity of it’s own or not is it’s clinical similarity with pustular psoriasis of the von Zumbusch type, the morphology of the pustules often being indistinguishable in both diseases. Many authors have addressed this issue and until now no clear-cut rules for the differentiation of both entities exist but a list of differences seems to justify the distinction between AGEP and pustular psoriasis (Table 1).
Subcorneal pustular dermatosis (Sneddon-Wilkinson)
Sneddon-Wilkinson disease is characterized by larger, flaccid blisters with hypopyon formation often arranged in a circinate distribution pattern. In addition, evolution of the disease is far less acute than in AGEP.
Bullous and/or pustular lesions may arise in purpura lesions of leucocytoclastic vasculitis. In addition there seems to be a special variant of leucocytoclastic vasculitis which is characterized by the development of many small pustules which – as opposed to AGEP – are localized mainly on the dorsum of the hands and which might also be drug-induced. A marked leucocytoclastic vasculitis can be detected in histology.10,11 Confusion may occur due to the report of some cases of pustular vasculitis under the term pustulosis acuta generalisata5,12 or due to the occasional presence of vasculitis in AGEP.
Drug hypersensitivity syndrome
Drug hypersensitivity syndrome, also referred to as DRESS (an acronym for drug rash with eosinophilia and systemic symptoms) may also show papulo-vesicles and/or papulo-pustules, the pustular component being usually less pronounced than in AGEP. In addition patients show fever, lymphadenopathy, eosinophilia, mononucleosis and often severe visceral involvement like hepatitis, nephritis, pneumonitis, and/or myocarditis.
Toxic epidermal necrolysis (TEN)
The presence of “atypical” target lesions and the confluence of pustules mimicking a positive Nikolsky-sign may suggest the diagnosis of TEN in severe cases of AGEP. In general the distinction can be easily made by experienced physicians as, among other criteria, epidermal detachment in AGEP is much more superficial, and mucous membrane involvement is much more pronounced in TEN. Whereas differentiation in some cases might be difficult on clinical grounds alone, histology is significantly different in TEN typically showing full thickness epidermal necrosis and only a very sparse inflammatory infiltrate. Yet, in our experience even some overlap cases might exist that fulfil the criteria for both diseases both clinically and histologically.
As a conclusion from a retrospective analysis of 63 cases the following five criteria have been suggested for the definition of AGEP: 1) several dozens of small, mostly non follicular pustules arising on a widespread edematous erythema; 2) histopathologic changes as described above; 3) fever (>38 °C); 4) blood neutrophil counts above 7×109/L; and 5) acute evolution with spontaneous resolution of pustules in less than 15 days.6 While performing a multinational epidemiological case-control study on severe cutaneous adverse reactions (EuroSCAR-project) we realized, that these criteria were not precise enough, especially when dealing with the retrospective assessment of cases. We therefore elaborated a more sophisticated scoring system presented in Table 2.
From the current data males and females seem to be equally affected and AGEP can occur at any age. In one study HLA B51, DR11 and DQ3 were found to be more frequent than in the average population.13 From the inclusion rate in the EuroSCAR study we estimate the incidence rate of AGEP to be in the range of 1 to 5 cases per million per year, but reliable data is missing.
Etiology and pathogenesis
It seems that more than 90% of cases with AGEP or toxic pustuloderma are drug induced. A wide range of drugs has been suspected of causing these reactions in case reports and larger series (Table 3A, B), antibacterials being the most frequent triggers. A high proportion of these cases have been attributed to aminopenicillins or macrolides but interestingly not to sulfonamides, who have a high potential of causing other cutaneous drug reactions. Also an increasing number of cases attributed to antimycotic drugs is being reported. In the group of non-antiinfective drugs especially calcium channel blockers, carbamazepine and paracetamol have been reported as culprit agents in several cases. In a minority of cases viral infections6,14–16 have been suspected to trigger AGEP.
After administration of a new drug it may take 1 to 3 weeks until – probably as result of a primary sensitization – skin symptoms arise. Yet there is a second group of patients where the interval between drug intake (especially antibacterials) and skin symptoms may be as short as a few hours to 2–3 days. Such rapid onsets have been described in patients who were rechallenged with the same drug after a first episode of AGEP or patients with a known previous sensitization to topical antibacterials. More often than in other drug reactions patch testing shows positive, sometimes strong and even pustular reactions.17 Furthermore in vitro tests like the macrophage migration inhibition factor (MIF) test and the mast cell degranulation (MCD) test have been shown to be helpful in detecting the causative drugs in AGEP (18). Although the mechanisms of AGEP have not been investigated some of the mentioned features suggest an immunologic recall phenomenon where in particular memory T cells producing neutrophil promoting cytokines like interleukin (IL)-3 and IL-8 play an important role.
Obviously the causative drug has to be discontinued and antibiotics are not to be given unless there is a clear and well-documented associated infection. Due to the benign, self-limited course of the disease a specific treatment, especially systemic corticosteroid treatment which is often taken into consideration is usually not necessary. Symptomatically systemic antipyretics can be given if not suspected as causative drug for the disease.