Diseases categorized as autoinflammatory keratinization diseases (AiKDs), and their pathologies and treatments.

Whole-exome and whole-genome sequencing have become widespread in approximately the last 15 years, and the predisposing factors and pathomechanisms of inflammatory keratinization diseases, which have been unknown for a long time, have gradually been revealed. Hence, various inflammatory keratinization diseases are recognized to cause innate immunity hyperactivation. Therefore, we have been advocating for the clinical entity, "autoinflammatory keratinization diseases (AiKDs)" since 2017. AiKDs are inflammatory keratinization diseases caused by autoinflammatory-related pathomechanisms in the skin. The aberrant activation of innate immunity and the resultant autoinflammation in the epidermis and the superficial dermis in AiKDs cause hyperkeratosis in the epidermis. Our initially proposed concept of AiKDs included generalized pustular psoriasis and related conditions, pityriasis rubra pilaris type V, and familial keratosis lichenoides chronica. Since then, the number of diseases known to be AiKDs has increased as previously unknown disease-causing factors and pathogenetic mechanisms of inflammatory keratinization diseases have been clarified one by one. To date, porokeratosis, hidradenitis suppurative, keratosis linearis with ichthyosis congenita and sclerosing keratoderma (KLICK) syndrome, and AiKDs associated with epidermal growth factor receptor (EGFR) deficiency or with hepatitis and autism have been recognized as AiKDs. The concept of AiKDs is considered extremely useful in our precise understanding of the pathogeneses behind inflammatory keratinization diseases and our appropriate treatment method selection. The number of AiKDs is expected to grow with the clarification of the pathomechanisms of further inflammatory keratinization diseases.

Trastornos autoinflamatorios de la queratinización / Autoinflammatory Keratinitzation Diseases

La enfermedad autoinflamatoria de la queratización (AiKD, por sus siglas en inglés) es un concepto clínico novedoso que engloba a las enfermedades que presentan antecedentes genéticos, así como mecanismos patogénicos mixtos de autoinflamación y autoinmunidad, lo que en su conjunto se traducirá en una queratinización aberrante de la piel. Los recientes avances han revelado causas genéticas y/o factores predisponentes para una serie de AiKD, dentro de los que se pueden enumerar la presencia de las mutaciones en el IL36RN, en relación con la psoriasis pustulosa, la acrodermatitis continua y la hidradenitis supurativa; en el CARD14, en relación con la pitiriasis rubra pilaris tipo V y algunas formas de psoriasis pustulosa, y en el NLRP1 en relación con la queratosis liquenoide crónica familiar (KLC, por sus siglas en inglés). Se sospecha que la fisiopatología de la AiKD también estaría presente en algunos trastornos no monogénicos. Se debe de comprender que existe una relación bidireccional entre la inflamación y la queratinización para poder determinar un tratamiento óptimo; así mismo para poder desarrollar nuevos fármacos ambos factores deben de tenerse en cuenta. Probablemente en los próximos años nuevas enfermedades inflamatorias de la queratinización serán incluidas dentro del grupo de las AiKD (AU)

Autoinflammatory keratinization disease (AiKD) is a novel clinical concept encompassing diseases with a genetic background and mixed pathogenic mechanisms of autoinflammation and autoimmunity, leading to an aberrant keratinization of the skin. Recent advances in medical genetics have revealed genetic causes and/or predisposing factors for a number of AiKD's, such as mutations in IL36RN related with pustular psoriasis, acrodermatitis continua and hidradenitis suppurativa, in CARD14 in pityriasis rubra pilaris type V and some forms of pustular psoriasis, and in NLRP1 related with familial keratosis lichenoides chronica (KLC). It is suspected that AiKD pathophysiology would also be involved in non-monogenic disorders. The bidirectional relationship between inflammation and keratinization should be understood in order to outline optimal management, and new drug development should take both targets into account. We assume that new inflammatory keratinization diseases may be recognized as AiKDs in the coming years (AU)

Erythema Ab Igne with Histological Features of Keratosis Lichenoides Chronica.

Erythema ab igne (EAI) is a localized, hyperpigmented and reticulated dermatosis at sites of chronic heat exposure. Within longstanding skin lesions of EAI, hyperkeratotic lesions may emerge and can potentially transform into pre-malignant or malignant skin lesions. A 55-year-old woman presented for the evaluation of multiple hyperkeratotic lesions along with a reticular patterned hyperpigmentation on her right knee, an area that had repeated and prolonged exposure to a heat source over a period of several months. Based on her clinical history and the physical examination of her lesions, she was diagnosed as having a hyperkeratotic form of EAI. A skin biopsy was performed to rule out malignant alteration, but the histopathological findings were supportive of keratosis lichenoides chronica.

Autoinflammatory keratinitzation diseases (AIKDs. / Trastornos autoinflamatorios de la queratinización.

Autoinflammatory keratinization disease (AiKD) is a novel clinical concept encompassing diseases with a genetic background and mixed pathogenic mechanisms of autoinflammation and autoimmunity, leading to an aberrant keratinization of the skin. Recent advances in medical genetics have revealed genetic causes and/or predisposing factors for a number of AiKD's, such as mutations in IL36RN related with pustular psoriasis, acrodermatitis continua and hidradenitis suppurativa, in CARD14 in pityriasis rubra pilaris type V and some forms of pustular psoriasis, and in NLRP1 related with familial keratosis lichenoides chronica (KLC). It is suspected that AiKD pathophysiology would also be involved in non-monogenic disorders. The bidirectional relationship between inflammation and keratinization should be understood in order to outline optimal management, and new drug development should take both targets into account. We assume that new inflammatory keratinization diseases may be recognized as AiKDs in the coming years.

Childhood-onset keratosis lichenoides chronica: A case report.

Keratosis lichenoides chronica (KLC) is a rare dermatosis which represents different clinical characteristics between adult- and pediatric-onset cases. We described a childhood case of KLC with features typical for adult-onset disease. Acitretin led to partial improvement of her skin, but not mucosal, lesions.

Erythema ab igne with features resembling keratosis lichenoides chronica.

Erythema ab igne (EAI) is an asymptomatic dermatosis that develops in response to chronic exposure to low-grade heat. Characteristic findings on histopathology include epidermal atrophy, dermal elastosis, atypical histiocytes, and melanin and hemosiderin deposition. Reactive endothelial changes and prominent vascular proliferation are variable. Keratosis lichenoides chronica (KLC) is a rare lichenoid hyperkeratotic dermatosis. Acanthosis with parakeratosis and a lichenoid interface dermatitis with lymphocytes, histiocytes, and plasma cells are characteristic findings of KLC. Although its etiology remains unclear, KLC has been reported to occur in response to heat. Herein, we report a case of EAI with features resembling KLC.

Autoinflammatory keratinization diseases: An emerging concept encompassing various inflammatory keratinization disorders of the skin.

Classifying inflammatory skin diseases is challenging, especially for the expanding group of disorders triggered by genetic factors resulting in hyperactivated innate immunity that result in overlapping patterns of dermal and epidermal inflammation with hyperkeratosis. For such conditions, the umbrella term "autoinflammatory keratinization diseases" (AIKD) has been proposed. AIKD encompasses diseases with mixed pathomechanisms of autoinflammation and autoimmunity, and includes IL-36 receptor antagonist (IL-36Ra)-related pustulosis, CARD14-mediated pustular psoriasis, pityriasis rubra pilaris (PRP) type V, and familial keratosis lichenoides chronica (KLC). Mechanistically, the entities include generalized pustular psoriasis (GPP) without psoriasis vulgaris, impetigo herpetiformis and acrodermatitis continua, which are IL-36Ra-related pustuloses caused by loss-of-function mutations in IL36RN; GPP with psoriasis vulgaris and palmoplantar pustular psoriasis which are CARD14-mediated pustular psoriasiform dermatoses with gain-of-function variants of CARD14; PRP type V which is caused by gain-of-function mutations in CARD14; and, familial KLC in which mutations in NLRP1, an inflammasome sensor protein predominantly expressed in skin, have been identified. It is likely that further inflammatory keratinization disorders will also fall within the concept of AIKD, as elucidation of novel pathogenic mechanisms of inflammatory keratinization diseases emerges. A better understanding of the pathophysiology of AIKD is likely to lead to innovative, targeted therapies that benefit patients.

Germline NLRP1 Mutations Cause Skin Inflammatory and Cancer Susceptibility Syndromes via Inflammasome Activation.

Inflammasome complexes function as key innate immune effectors that trigger inflammation in response to pathogen- and danger-associated signals. Here, we report that germline mutations in the inflammasome sensor NLRP1 cause two overlapping skin disorders: multiple self-healing palmoplantar carcinoma (MSPC) and familial keratosis lichenoides chronica (FKLC). We find that NLRP1 is the most prominent inflammasome sensor in human skin, and all pathogenic NLRP1 mutations are gain-of-function alleles that predispose to inflammasome activation. Mechanistically, NLRP1 mutations lead to increased self-oligomerization by disrupting the PYD and LRR domains, which are essential in maintaining NLRP1 as an inactive monomer. Primary keratinocytes from patients experience spontaneous inflammasome activation and paracrine IL-1 signaling, which is sufficient to cause skin inflammation and epidermal hyperplasia. Our findings establish a group of non-fever inflammasome disorders, uncover an unexpected auto-inhibitory function for the pyrin domain, and provide the first genetic evidence linking NLRP1 to skin inflammatory syndromes and skin cancer predisposition.

Keratosis lichenoides chronica: Case-based review of treatment options.

Keratosis lichenoides chronica (KLC) is a rare dermatological condition characterized by keratotic papules arranged in a parallel linear or reticular pattern and facial lesions resembling seborrheic dermatitis or rosacea. The clinical, histological and therapeutic information on 71 patients with KLC retrieved through a PubMed search plus one our new case were analyzed. KLC affects patients of all ages, with a modest male predominance. Pediatric cases represent about one quarter of patients. Diagnosis is usually delayed and histologically confirmed. All patients have thick, rough and scaly papules and plaques arranged in a linear or reticular pattern, on limbs (>80%) and trunk (about 60%). Face involvement is described in two-thirds of patients. Lesions are usually asymptomatic or mildly pruritic. Other manifestations, such as palmoplantar keratoderma, mucosal involvement, ocular manifestations, nail dystrophy, are reported in 20-30% of patients. Children present more frequently alopecia. No controlled trials are available. Results from small case series or single case reports show that the best treatment options are phototherapy and systemic retinoids, alone or in combination, with nearly half of patients reaching complete remission. Systemic corticosteroids as well as antibiotics and antimalarials are not effective.

A Mild Case of Adult-Onset Keratosis Lichenoides Chronica Successfully Treated with Narrow-Band UVB Monotherapy.

Keratosis lichenoides chronica (KLC) is a rare keratotic disorder of unknown origin. Effective treatment has not been established yet. Here, we present adult-onset KLC, which was treated by narrow-band ultraviolet B (NB-UVB) monotherapy. Although NB-UVB was reported to be effective for pediatric-onset KLC, it has not been clear if this regimen is also useful for adult-onset type because pediatric-onset KLC is suggested to be different in nature. We assume that KLC is treatable by NB-UVB regardless of the age of the patient.

Keratosis Lichenoides Chronica with Pachyonychia Congenita-like Nail Changes

A 26-year-old man presented with a 7-month history of hyperkeratotic skin lesions on both elbows and heels. He also had marked subungal hyperkeratosis and splinter hemorrhage on the finger and toe nails. A biopsy specimen from the elbow revealed lichenoid re-actions with areas of epidermal atrophy with alternating acanthosis and foci of parakeratosis. We made a diagnosis of keratosis lichenoides chronica based on the characteristic clinicopathologic findings. We have treated the patient with etretinate, but only the skin lesions on the elbows and heels responded to treatment.

Unilateral Keratosis Lichenoides Chronica

Keratosis lichenoides chronica is rare chronic dermatosis characterized by progressive development of licheniod papulonodules especially on the extremities and trunk. A 15-year-old male patient had erythematous to violaceous scaly patches and plaques on the left side of trunk and lower extremity along Blaschko's lines. Clinical and histologic findings were compatible with keratosis lichenoides chronica showing unilateral distribution.