Distinguishing pustular psoriasis and acute generalized exanthematous pustulosis on the basis of plasmacytoid dendritic cells and MxA protein

IL-36-driven pustulosis: Transcriptomic signatures match between generalized pustular psoriasis (GPP) and acute generalized exanthematous pustulosis (AGEP)

BACKGROUND

Due to similarities, the distinction between generalized pustular psoriasis (GPP) and acute generalized exanthematous pustulosis (AGEP) has been a matter of debate for a long time.

OBJECTIVES

Our aim was to define the molecular features of GPP and AGEP.

METHODS

We analyzed skin biopsy samples and clinical data from 125 patients with AGEP, GPP, palmoplantar pustulosis (PPP), plaque psoriasis (PSO), and nonpustular cutaneous adverse drug reactions (ADRs), as well as from healthy skin controls using RNA-sequencing and blinded histopathologic analyses.

RESULTS

The transcriptome and histopathologic features of AGEP and GPP samples exhibited significant overlap (177 differentially expressed genes [DEGs] in GPP and AGEP compared to healthy skin, only 2 DEGs comparing AGEP and GPP). Yet, they displayed marked differences from those of PPP, PSO, and ADR samples, with a notable number of DEGs (131 DEGs comparing AGEP and PSO, 75 DEGs comparing AGEP and PPP, and 52 DEGs comparing AGEP and ADR). A transcriptome profile subgroup evaluation of >13,000 analyzed genes did not reveal any DEGs in drug-induced GPP and AGEP. Moreover, the immune response pattern and immune cell composition did not differ between drug-induced GPP and AGEP, whereas non-drug-induced GPP had higher expression of TH17-cell-related genes and a higher neutrophil count than AGEP.

CONCLUSIONS

We propose that AGEP is a drug-induced variant of GPP and therefore part of IL-36-related pustulosis. A key signature overarching this spectrum was identified, thereby opening the therapeutic approach of IL-36 inhibition to all subtypes of the disease.

NETosis of psoriasis: a critical step in amplifying the inflammatory response

NETosis, a regulated form of neutrophil death, is crucial for host defense against pathogens. However, the release of neutrophil extracellular traps (NETs) during NETosis can have detrimental effects on surrounding tissues and contribute to the pro-inflammatory response, in addition to their role in controlling microbes. Although it is well-established that the IL-23-Th17 axis plays a key role in the pathogenesis of psoriasis, emerging evidence suggests that psoriasis, as an autoinflammatory disease, is also associated with NETosis. The purpose of this review is to provide a comprehensive understanding of the mechanisms underlying NETosis in psoriasis. It will cover topics such as the formation of NETs, immune cells involved in NETosis, and potential biomarkers as prognostic/predicting factors in psoriasis. By analyzing the intricate relationship between NETosis and psoriasis, this review also aims to identify novel possibilities targeting NETosis for the treatment of psoriasis.

Eosinophils in psoriasis: A systematic review and meta-analysis introducing a study quality assessment tool for diagnostic pathology studies

BACKGROUND

The histopathologic features of psoriasis are well-documented, but recent studies have highlighted atypical features, such as eosinophils, in clinically confirmed cases.

METHODS

A systematic review exploring eosinophils in psoriasis was performed. A novel quality assessment tool (SQAT-Path) we designed for cross-sectional pathology studies was employed.

RESULTS

Five studies (N = 218) were identified. The pooled prevalence of dermal eosinophils in psoriasis was 46% (95% confidence interval, 0.27-0.66). The prevalences of 1 to 5 lesional eosinophils (24%) compared to >5 eosinophils (26%) were similar. There was no association between eosinophils and prior treatment. There was also no association between eosinophils and spongiosis. In SQAT-Path, studies scored between 9 and 18 (out of a maximum of 27: "fair" to "good"), consistent with the ratings using other assessment tools.

CONCLUSION

Eosinophils were found in approximately half of systematically studied and published cases of psoriasis. When present, their quantity is variable, with the likelihood of having greater than 5 eosinophils in a biopsy section comparable to having between 1 and 5. Greater than 5 eosinophils, as an isolated finding, would not be typical of psoriasis, but should not preclude its diagnosis without considering the overall histologic context.

Dynamics of a network mediated by IL-36 and involved in the pathogenesis of psoriasis

The pathogenesis of the inflammatory, chronic, and common skin disease psoriasis involves immune cells, skin cells (keratinocytes), and the cytokines they secrete. Hyperproliferation and abnormal differentiation of keratinocytes are hallmarks of the disease. The roles of cytokines such as TNFα, IL-15, IL-17, and IL-23 in psoriasis have been studied through mathematical/computational models as well as experiments. However, the role of proinflammatory cytokine IL-36 in the onset and progression of psoriasis is still elusive. To explore the role of IL-36, we construct a network embodying indirect cell-cell interactions of a few immune and skin cells mediated by IL-36 based on existing knowledge. We also develop a mathematical model for the network and perform a global sensitivity analysis. Our results suggest that the model is most sensitive to a parameter that represents the level of cytokine IL-36. In addition, a steady-state analysis of the model suggests that an increase in the level of IL-36 could lead to the hyperproliferation of keratinocytes and, thus, psoriasis. Our analysis also highlights that the plaque formation and progression of psoriasis could occur through either a gradual or a switch-like increase in the keratinocyte population. We propose that the switch-like increase would be due to a bistable behavior of the network toward either a psoriatic or healthy state and could be used as a novel treatment strategy.

The role of eosinophils in the differential diagnosis of inflammatory skin diseases

Eosinophils are known to be present in inflammatory skin diseases, but their diagnostic utility is not well established. Upon review of the published status of lesional eosinophils, several categories were identified. 1) Lesional eosinophils highly characteristic such that, in their absence, the pathologist may question the diagnosis. These include arthropod bite reactions and scabies, urticarial dermatitis, and other eosinophilic dermatoses. 2) Lesional eosinophils rare or absent, such that, in their presence, the pathologist may question the diagnosis. These include pityriasis lichenoides, graft versus host disease, and connective tissue disorders. 3) Lesional eosinophils variable and, while in some cases expected, are not required for diagnosis. These include drug reactions, atopic dermatitis and allergic contact dermatitis. 4) Lesional eosinophils variable and not expected but may be seen to a limited extent. These include lichen planus and psoriasis.

Type 1 interferon signature and cytotoxic T lymphocyte activation targeted against sweat ducts in inflammatory acquired idiopathic generalized anhidrosis

BACKGROUND

Acquired idiopathic generalized anhidrosis (AIGA) leads to heat intolerance due to the loss or reduction in thermoregulatory sweating over an extensive area of the body. The pathomechanism of AIGA is still unclear but is believed to be autoimmune.

OBJECTIVES

We investigated the clinical and pathological features of inflammatory AIGA (InfAIGA) and noninflammatory AIGA (non-InfAIGA) within the skin.

METHODS

We compared anhidrotic and normohidrotic skin samples from 30 patients with InfAIGA and non-InfAIGA, as well as skin samples of melanocytic nevus as a negative control. We conducted morphometric analysis and immunohistochemical analysis of cell types and expression of inflammatory molecules (TIA1, CXCR3 and MxA). MxA expression was used as a proxy for type 1 interferon activity.

RESULTS

We found that tissue samples from patients with InfAIGA exhibited inflammation within the sweat duct and atrophy of the sweat coil, whereas patients with non-InfAIGA exhibited only atrophy of the sweat coil. Cytotoxic T lymphocyte infiltration and MxA expression were only observed in the sweat ducts of patients with InfAIGA.

CONCLUSIONS

InfAIGA is associated with increased sweat duct inflammation and sweat coil atrophy, whereas non-InfAIGA is only associated with sweat coil atrophy. These data suggest that inflammation leads to epithelial destruction of sweat ducts associated with the sweat coil atrophy and subsequent loss of function. Non-InfAIGA may be regarded as a postinflammatory state of InfAIGA. These observations indicate the contribution of both type 1 and type 2 interferons to sweat gland injury. The mechanism involved is similar to the pathomechanism of alopecia areata (AA).

Acute Generalized Exanthematous Pustulosis: Clinical Features, Differential Diagnosis, and Management

Acute generalized exanthematous pustulosis (AGEP) is a rare, acute, severe cutaneous adverse reaction mainly attributed to drugs, although other triggers, including infections, vaccinations, ingestion of various substances, and spider bites, have also been described. AGEP is characterized by the development of edema and erythema followed by the eruption of multiple punctate, non-follicular, sterile pustules and subsequent desquamation. AGEP typically has a rapid onset and prompt resolution within a few weeks. The differential diagnoses for AGEP are broad and include infectious, inflammatory, and drug-induced etiologies. Diagnosis of AGEP depends on both clinical and histologic criteria, as cases of overlap with other disease processes have been reported. Management includes removal of the offending drug or treatment of the underlying cause, if necessary, and supportive care, as AGEP is a self-limited disease. This review aims to provide an overview and update on the epidemiology, pathogenesis, reported precipitating factors, differentials, diagnosis, and management of AGEP.

A Case of Acute Generalized Exanthematous Pustulosis Induced by Ceftriaxone

Acute generalized exanthematous pustulosis (AGEP) is a rare and severe skin disorder induced in more than 90% of cases by an adverse drug reaction. This condition is defined by an acute growth of numerous, pin-head-sized, non-follicular pustules on a background of edematous erythema that starts on the face or in the armpits and groin. It is accompanied by fever and increased inflammatory markers. We present a case of a 39-year-old male, admitted to the internal medicine department due to Streptococcus pneumoniae meningitis treated with ceftriaxone, who developed erythema covered with small sterile pustules in the face, neck, and axilla four days after antibiotic treatment. The clinical and pathological correlations confirmed the diagnosis, and the dermatosis resolved after discontinuing the drug and systemic corticosteroid treatment. Early recognition of this drug-induced dermatosis is crucial for adequate treatment.

Mannan-binding lectin exacerbates the severity of psoriasis by promoting plasmacytoid dendritic cell differentiation via the signal transducer and activator of transcription 3-interferon regulatory factor 8 axis

Psoriasis is a chronic inflammatory skin disease mediated by host immune responses. Plasmacytoid dendritic cells (pDC) and interferon (IFN)-α secreted by pDC are involved in the initiation of psoriasis. Mannan-binding lectin (MBL), a vital component of the complement pathway, plays a critical role in innate immune defense and the inflammatory response. Our previous study found that MBL could exacerbate skin inflammation in psoriatic mice, but the effect of MBL on pDC remains unstudied. Herein, we revealed that the circulating level of MBL was elevated in patients with psoriasis compared with the healthy controls. Moreover, the MBL level was positively correlated with disease severity, relative inflammatory cytokine levels, and peripheral blood (PB) pDC frequency in psoriasis. An in vitro study determined that the MBL protein could promote the differentiation of human pDC and upregulate the production of relative inflammatory cytokines and chemokines. Additionally, MBL-deficient (MBL^-/- ) mice exhibited decreased accumulation of pDC in lymph nodes, spleens, and skin lesions with reduced secretion of pDC-related cytokines compared with wild-type (WT) mice in the preliminary stage of psoriasis induced by imiquimod. Notably, the differentiation of pDC from bone marrow (BM) cells derived from MBL^-/- mice was weakened compared with that from WT mice upon Fms-like tyrosine kinase 3 ligand (Flt3L) incubation. Mechanistic research indicated that the signal transducer and activator of transcription 3 (STAT3)-interferon regulatory factor 8 (IRF8) axis was responsible for MBL-modulated pDC differentiation. In summary, these results suggest that MBL exacerbates the severity of psoriasis by enhancing pDC differentiation and pDC-related cytokine secretion via the STAT3-IRF8 axis, thus providing a new target for psoriasis treatment.

Pustular Psoriasis: From Pathophysiology to Treatment

Pustular psoriasis (PP) is a clinicopathological entity encompassing different variants, i.e., acute generalized PP (GPP), PP of pregnancy (impetigo herpetiformis), annular (and circinate) PP, infantile/juvenile PP, palmoplantar PP/palmoplantar pustulosis, and acrodermatitis continua of Hallopeau (ACH), which have in common an eruption of superficial sterile pustules on an erythematous base. Unlike psoriasis vulgaris, in which a key role is played by the adaptive immune system and interleukin (IL)-17/IL-23 axis, PP seems to be characterized by an intense inflammatory response resulting from innate immunity hyperactivation, with prominent involvement of the IL-36 axis. Some nosological aspects of PP are still controversial and debated. Moreover, owing to the rarity and heterogeneity of PP forms, data on prognosis and therapeutic management are limited. Recent progresses in the identification of genetic mutations and immunological mechanisms have promoted a better understanding of PP pathogenesis and might have important consequences on diagnostic refinement and treatment. In this narrative review, current findings in the pathogenesis, classification, clinical features, and therapeutic management of PP are briefly discussed.

Acute Generalized Exanthematous Pustulosis Induced by Cetuximab

A wide variety of diseases and drugs can cause cutaneous pustular eruptions. Acute generalized exanthematous pustulosis (AGEP) is a unique drug-induced dermatosis clinically presented as erythematous papular and pustular eruption, usually caused by certain systemic drugs. We are presenting a very rare association of AGEP with a biological agent, cetuximab. A male aged 66 years, who was recently diagnosed with a case of squamous cell carcinoma of glottis, presented in the dermatology clinic with a recent onset of fever and widespread pustular eruption over the face, trunk, and limbs. The eruption was noted after the injection of cetuximab given for his squamous cell carcinoma. The clinical history, typical physical findings, and histopathological features confirm the diagnosis of AGEP. The injection cetuximab was stopped and the patient was treated with some topical and systemic medications and the symptoms resolved completely in a few weeks. Our case is an interesting clinical presentation of AGEP due to cetuximab therapy and confirms that this is an extremely rare and proven adverse effect of cetuximab. To our knowledge, this is the first-ever reported case of AGEP associated with cetuximab. Physicians need to be aware of this unique but important side effect of cetuximab and perform a proper physical examination and specific investigations that can be useful to reach a final diagnosis. 

Diagnostic utility of plasmacytoid dendritic cells in dermatopathology

Differentiating cutaneous diseases that mimic each other clinically and histopathologically can at times be a challenging task for the dermatopathologist. At the same time, differentiation of entities with overlapping features may be crucial for patient management. Although not seen in normal skin, plasmacytoid dendritic cells usually infiltrate the skin in several infectious, inflammatory/autoimmune and neoplastic entities. Plasmacytoid dendritic cells can be identified in tissue using specific markers such as CD123 and/or blood-derived dendritic cell antigen-2. Plasmacytoid dendritic cells are the most potent producers of type I interferons and their activity may therefore be assessed indirectly in tissue using human myxovirus resistance protein A, a surrogate marker for type I interferon production. In recent years, accumulating evidence has established the utility of evaluating for specific plasmacytoid dendritic cell-related parameters (plasmacytoid dendritic cell content, distribution and clustering and/ or human myxovirus resistance protein A expression) as a diagnostic tool in differentiating cutaneous diseases with overlapping features such as the alopecias, lupus and its mimics, and neoplastic entities. In this review, we provide an update on the current evidence on this topic and on the contexts where this can be a useful adjunct to reach the histopathological diagnosis.

Clinical Presentation and Management of Atypical and Recalcitrant Acute Generalized Exanthematous Pustulosis (AGEP)

Acute generalized exanthematous pustulosis (AGEP) is a severe cutaneous adverse reaction (SCAR) characterized by sterile non-follicular pustules on an erythematous base that form rapidly after drug exposure. AGEP is mediated by numerous cytokines produced by drug specific T-cells that mediate neutrophilic intracorneal, subcorneal, and/or intraepidermal pustule development. Though genetic susceptibility is not fully understood, individuals with mutations in IL-36RN may be at increased risk of AGEP development. AGEP commonly presents with leukocytosis and fever in the acute pustular phase and follows a self-limited desquamative recovery phase upon removal of offending drug. Severe cases of AGEP may have multisystem organ involvement. Atypical presentations of AGEP include localized eruptions and cases with overlapping clinical and histopathological features associated with Stevens-Johnson syndrome/toxic epidermal necrolysis, drug reaction with eosinophilia and systemic symptoms, and generalized pustular psoriasis. Most cases of AGEP clear rapidly with systemic corticosteroids, but severe or recalcitrant cases may require other systemic therapies such as cyclosporine, and intravenous immunoglobulin.

Plasmacytoid dendritic cells in keratoacanthoma and squamous cell carcinoma: A blinded study of CD123 as a diagnostic marker

BACKGROUND

Histopathologic distinction between keratoacanthoma (KA) and squamous cell carcinoma (SCC) is challenging. We surmised that a discriminatory immunostain would be clinically meaningful. Previous investigators have found CD123-positive plasmacytoid dendritic cells (PDCs) are more prominent in KA than SCC. We sought to determine if CD123 immunostaining might have value as a diagnostic test for distinguishing KA from SCC.

METHODS

We used blinded, semi-automated image analysis to compare CD123 expression in 66 KAs and 63 SCCs in a tissue microarray.

RESULTS

PDCs were present in both KA and SCC. Mean PDC frequency was higher in KA than SCC (14.2 vs 11.2 mean cells/0.0945 square mm) but the difference was not statistically significant (P = 0.1240). There was no significant difference in mean PDC cluster frequency, mean intratumoral PDC frequency, or the percentage of PDCs as proportion of the total mononuclear inflammatory cell infiltrate between KA and SCC.

CONCLUSION

CD123 immunostaining is not a clinically useful test for distinguishing KA from SCC.