# Internal Medicine/Immunologically Mediated Skin Diseases
## Pemphigus Vulgaris

Pemphigus vulgaris is a rare and severe autoimmune blistering disorder characterized by the production of autoantibodies, primarily of the IgG class, targeting desmoglein 3, a critical protein responsible for maintaining cell adhesion in the epidermis. This autoimmune response leads to the disruption of desmosomes, specialized adhesive structures that bind adjacent skin cells together. Consequently, the weakened cell adhesion results in the formation of painful, flaccid blisters on the skin and mucous membranes.
The blisters in pemphigus vulgaris are notoriously fragile and prone to rupture, leaving behind excruciating erosions. These erosions can be widespread and affect areas such as the oral mucosa, throat, genitals, and even the eyes. The disease primarily affects adults, with a peak incidence between the ages of 40 and 60.
Diagnosing pemphigus vulgaris involves a meticulous clinical evaluation, often necessitating multiple skin biopsies, immunofluorescence studies, and serological tests to detect the presence of autoantibodies. Early diagnosis is crucial, as prompt initiation of treatment significantly impacts the prognosis.
Management of pemphigus vulgaris is intricate and multifaceted, involving aggressive immunosuppressive therapies to curb the autoimmune response. High-dose systemic corticosteroids are typically the initial treatment of choice to control the rampant inflammation. However, prolonged corticosteroid use can lead to a plethora of debilitating side effects, necessitating the introduction of other immunosuppressive drugs such as azathioprine, mycophenolate mofetil, or rituximab. Simultaneously, meticulous wound care and infection prevention measures are paramount to prevent secondary infections and complications.

## Pemphigus Foliaceus

Pemphigus foliaceus stands as a distinct autoimmune blistering disorder separate from pemphigus vulgaris. In this condition, autoantibodies predominantly target desmoglein 1, a protein that plays a pivotal role in cell adhesion in the upper layers of the epidermis.
The pathophysiology of pemphigus foliaceus revolves around the binding of autoantibodies to desmoglein 1. This leads to the disruption of cell adhesion in the superficial layers of the epidermis, resulting in blister formation in the epidermis without mucous membrane involvement. These blisters are typically shallow, flaccid, and prone to rupture, resulting in crusted erosions.
Treatment for pemphigus foliaceus closely mirrors that of pemphigus vulgaris and encompasses corticosteroids and immunosuppressive medications. In localized cases, topical treatments may prove effective. The primary goal is to control blistering, minimize complications, and enhance the patient's overall quality of life.

## Paraneoplastic Pemphigus

Paraneoplastic pemphigus is an exceedingly rare blistering disorder with a robust association with malignancies, particularly hematologic cancers like lymphomas. This condition is characterized by the development of painful oral and skin erosions. One of the distinctive challenges in managing paraneoplastic pemphigus is its direct link to underlying cancers. Therefore, alongside treating the skin and mucous membrane symptoms, addressing the malignancy itself is an indispensable component of management. Immunosuppressive therapies, including corticosteroids, may be necessary to control skin manifestations.

## Bullous Pemphigoid

Bullous pemphigoid, predominantly affecting elderly individuals, typically over the age of 60, is characterized by the development of large, tense blisters that do not rupture easily. Autoantibodies in bullous pemphigoid target proteins within the basement membrane zone, a crucial skin layer responsible for anchoring the epidermis to the underlying dermis. Unlike pemphigus, bullous pemphigoid generally spares mucous membranes.
The pathophysiology of bullous pemphigoid revolves around the binding of autoantibodies to two main antigens: BP180 (also known as collagen XVII) and BP230, both of which are components of the hemidesmosome, a structure essential for anchoring the epidermis. This binding initiates complement activation, inflammation, and ultimately blister formation.
Diagnosis of bullous pemphigoid includes a comprehensive clinical evaluation, skin biopsies, immunofluorescence studies, and serological tests to detect the presence of autoantibodies. Early diagnosis is critical to initiate treatment effectively.
Treatment of bullous pemphigoid revolves around reducing inflammation, primarily through systemic corticosteroids to suppress the immune response. In some cases, immunosuppressive medications like azathioprine or mycophenolate mofetil may be added to enable a reduction in corticosteroid dosage. Rigorous wound care is vital to prevent infections in areas affected by blisters.

## Pemphigoid Gestationis

Pemphigoid gestationis, also known as gestational pemphigoid or herpes gestationis, is an infrequent autoimmune blistering disorder that manifests during pregnancy or postpartum. It results in intensely pruritic, blistering eruptions, primarily on the abdomen but potentially affecting other body parts as well. The underlying cause is autoimmunity, with autoantibodies targeting proteins within the basement membrane zone.
Diagnosis of pemphigoid gestationis entails comprehensive clinical evaluation, skin biopsies, immunofluorescence studies, and serological tests. Treatment often involves topical corticosteroids and oral antihistamines to manage the relentless itching. In more severe cases, systemic corticosteroids may be necessary, although their use during pregnancy requires a meticulous consideration of risks and benefits.

## Dermatitis Herpetiformis

Dermatitis herpetiformis is a persistent blistering skin condition intricately associated with celiac disease, an autoimmune disorder triggered by the consumption of gluten-containing foods. It presents with intensely pruritic, grouped papules and blisters, typically distributed symmetrically on the extensor surfaces of the elbows, knees, buttocks, and lower back.
The hallmark feature of dermatitis herpetiformis is its robust association with gluten sensitivity. In essence, the autoimmune response underlying dermatitis herpetiformis is triggered by gluten consumption and mediated by the formation of IgA autoantibodies. These autoantibodies target transglutaminase 3, an enzyme involved in epidermal cell adhesion, leading to blister formation.
Diagnosing dermatitis herpetiformis necessitates skin biopsies, direct immunofluorescence studies, and serological tests to detect celiac-specific antibodies. Treatment primarily involves strict adherence to a gluten-free diet, which effectively controls both the skin and gastrointestinal symptoms associated with celiac disease. Additionally, medications like dapsone or sulfapyridine may be prescribed to alleviate skin manifestations.

## Linear IgA Disease

Linear IgA disease is a rare autoimmune blistering disorder characterized by the linear deposition of IgA antibodies along the basement membrane zone of the skin and mucous membranes. Clinically, it presents with tense blisters, often arranged in a linear fashion, and erosions on the skin and mucous membranes.
The pathogenesis of linear IgA disease centers around the production of IgA autoantibodies targeting various antigens within the basement membrane zone. While the exact cause remains unknown, this autoimmune response results in inflammation and blister formation.
Diagnosis of linear IgA disease involves skin biopsies, direct immunofluorescence studies, and serological tests. Treatment typically includes dapsone, a medication with anti-inflammatory and immunosuppressive properties. In severe cases or when dapsone is not tolerated, other immunosuppressive agents may be considered.

## Epidermolysis Bullosa Acquisita

Epidermolysis bullosa acquisita is a rare autoimmune blistering disorder characterized by autoantibodies targeting type VII collagen, a critical component of anchoring fibrils in the skin's basement membrane zone. These fibrils play a crucial role in maintaining skin integrity by anchoring the epidermis to the underlying dermis.
The pathophysiology of epidermolysis bullosa acquisita revolves around the formation of autoantibodies that bind to type VII collagen, leading to complement activation, inflammation, and blister formation. This condition typically manifests as tense blisters on trauma-prone areas of the skin.
Diagnosis of epidermolysis bullosa acquisita involves skin biopsies, direct immunofluorescence studies, and serological tests to detect autoantibodies against type VII collagen. Treatment can be challenging and often includes immunosuppressive medications to manage inflammation and blistering.

## Mucous Membrane Pemphigoid

Mucous membrane pemphigoid (MMP), also known as cicatricial pemphigoid, primarily affects mucous membranes, such as those in the mouth, eyes, throat, and genitals. It results in chronic scarring and can lead to severe complications if left untreated.
The pathophysiology of MMP involves autoantibodies targeting proteins within the basement membrane zone of mucous membranes. This autoimmune response leads to inflammation, blistering, and scarring. Diagnosis often requires biopsies of affected mucous membranes and immunofluorescence studies. Treatment is essential to prevent complications and may include immunosuppressive agents like corticosteroids, dapsone, or rituximab.

## Dermatomyositis

Dermatomyositis is an autoimmune disease that primarily affects the skin and muscles. Skin manifestations include a distinctive rash, often referred to as the "heliotrope rash," which appears as a purple-red discoloration on the upper eyelids and periorbital area. Other skin findings include erythematous or violaceous plaques on the upper trunk, back, and extremities, along with Gottron's papules on the knuckles. Dermatomyositis can also be associated with muscle weakness and inflammation.
The pathophysiology of dermatomyositis involves an autoimmune response against muscle and skin tissue. The exact cause is unknown, but it is thought to involve both genetic and environmental factors. Treatment includes corticosteroids, immunosuppressive medications, and physical therapy to manage muscle weakness and skin symptoms.

## Lupus Erythematosus

Lupus erythematosus is a complex autoimmune disorder that can affect various organs, including the skin. Cutaneous lupus erythematosus (CLE) encompasses a range of skin manifestations, from acute to chronic forms. Acute cutaneous lupus erythematosus typically presents with a butterfly-shaped rash on the face (malar rash) and is associated with systemic lupus erythematosus (SLE). Subacute cutaneous lupus erythematosus presents with scaly, coin-shaped lesions on sun-exposed areas of the skin. Chronic cutaneous lupus erythematosus includes discoid lupus erythematosus (DLE), which presents with erythematous plaques, follicular plugging, and atrophy, often leading to scarring.
The pathophysiology of lupus erythematosus involves a complex interplay of genetic predisposition, environmental triggers, and dysregulation of the immune system. Autoantibodies, such as anti-nuclear antibodies (ANA) and anti-double-stranded DNA antibodies, play a crucial role in the disease process. Treatment varies depending on the type and severity of lupus erythematosus but often includes corticosteroids, immunosuppressive medications, and lifestyle modifications to manage symptoms and prevent flares.

## Scleroderma and Morphea

Scleroderma, also known as systemic sclerosis, is a rare autoimmune disease characterized by the abnormal accumulation of collagen in the skin and various internal organs. It can be classified into two main categories: limited cutaneous scleroderma and diffuse cutaneous scleroderma. Limited cutaneous scleroderma primarily affects the skin of the fingers, face, and extremities, causing skin tightening and thickening. It is often associated with Raynaud's phenomenon, where the fingers and toes turn white, blue, or purple in response to cold or stress.
Diffuse cutaneous scleroderma involves more extensive skin thickening that can affect the trunk and internal organs, such as the lungs, heart, and gastrointestinal tract. This form of scleroderma is often more severe and can lead to significant organ dysfunction.
Morphea, on the other hand, is a localized form of scleroderma that primarily affects the skin. It presents as hardened, discolored patches on the skin that are typically oval or linear in shape. These patches can range in size from small to large and often have an ivory or purplish center with a lighter, halo-like border. Unlike systemic sclerosis, morphea typically does not affect internal organs.
The exact cause of scleroderma and morphea is not fully understood, but they are believed to involve a combination of genetic, environmental, and immune system factors. Treatment aims to manage symptoms, prevent complications, and slow disease progression. It may include medications to reduce inflammation and fibrosis, physical therapy to maintain joint mobility, and lifestyle modifications to address Raynaud's phenomenon.