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Pathology - Lichen planus Definition • An inflammatory dermatosis characterized by pruritic purple papules clinically and a lichenoid response pattern histologically. Epidemiology • Affects around 1% of the population. • Typically occurs in middle-aged people, with a slight prevalence in females. Aetiology: Unknown. Pathogenesis • Believed to signify a delayed-type hypersensitivity response to an unidentified epidermal antigen. Presentation • The cutaneous lesions are diminutive, flat-topped, violaceous papules that are typically associated with acute pruritus. • Delicate white lines (Wickham’s striae) typically traverse the surface. • The lesions predominantly manifest on the flexor surfaces of the wrists, the extensor surfaces of the hands, and the forearms. • Oral involvement is prevalent (see p. 86), as are genital lesionsespecially in males. Histopathology • A substantial band-like inflammatory infiltrate comprising lymphocytes and macrophages is observed beneath the epidermis. • The basal layer of the epidermis exhibits vacuolar damage accompanied by cytoid body formation and melanin leakage. • The epidermis demonstrates irregular acanthosis, hyperkeratosis, and wedge-shaped hypergranulosis. Prognosis: In the majority of instances, the condition resolves autonomously over a variable duration ranging from weeks to one year. 
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Pathology- Psoriasis Definition • A chronic, recurrent dermatological condition characterized by aberrant hyperproliferation of the epidermis. Epidemiology • Prevalent, impacting approximately 2% of the population. • Average age of onset is 25 years. Aetiology Current evidence indicates that psoriasis arises from an aberrant immune response to an environmental trigger in a genetically predisposed individual. • Factors recognized to provoke or intensify the disease encompass stress, infections, climate, alcohol consumption, smoking, and trauma. Genome-wide linkage study has identified a minimum of nine chromosomal loci linked to psoriasis, predominantly comprising genes that encode HLA proteins, cytokines, or cytokine receptors. Pathogenesis Activated plasmacytoid dendritic cells in the skin travel to draining lymph nodes, where they facilitate the differentiation of naïve T-cells into type 1 and type 17 helper and cytotoxic T-cells. Effector T-cells migrate to the skin, where they produce cytokines such as IL-17, IL-22, IFN-γ, and TNF-α, which promote the hyperproliferation of epidermal keratinocytes. The typical presentation of psoriasis features well-defined erythematous oval plaques adorned with adhering silvery scales. The preferred locations are the elbows, knees, and scalp. Nail involvement frequently presents with pitting and onycholysis. Guttate psoriasis is a clinical variation distinguished by tiny, erythematous papules measuring 1–5mm in size. Numerous instances are preceded by streptococcal infection. Severe psoriasis can lead to erythroderma (erythrodermic psoriasis). Histopathology Typical lesions exhibit psoriasiform epidermal proliferation accompanied by thinning of the suprapapillary plates. Plaques of parakeratosis exhibit a reduction of the granular layer underlying the parakeratosis. Collections of neutrophils are observed in the stratum corneum (Munro microabscesses) and may also be present inside the stratum spinosum. The dermis comprises dilated capillaries and an inflammatory infiltrate. Prognosis • Typically follows a chronic trajectory. • Can substantially affect quality of life.  Pathology – Eczemas Definition • A collection of inflammatory dermatoses clinically identified by an erythematous papulovesicular eruption and histologically defined by intraepidermal edema (spongiosis). Atopic dermatitis • Chronic dermatitis prevalent in individuals with atopy. • A highly prevalent condition with incidence rates reaching up to 15%. • Generally manifests in newborns and children. • Clinically induces a pruritic erythematous papulovesicular eruption affecting the facial region and the extensor surfaces of the upper and lower limbs. Biopsies from acute lesions reveal epidermal spongiosis and dermal inflammation. Biopsies from subsequent lesions demonstrate epidermal thickening and hyperkeratosis accompanied by moderate spongiosis. Contact dermatitis due to irritants • Inflammatory dermatosis induced by the direct toxic impact of an irritant. • A prevalent etiology of occupational dermatosis. • Clinically induces erythema accompanied by vesiculation. Biopsies reveal epidermal spongiosis and dermal inflammation. Allergic contact dermatitis • Inflammatory dermatosis resulting from a delayed-type hypersensitivity response to an allergen to which the patient has been exposed. • A prevalent occupational dermatosis, notably documented among hairdressers. • Clinically induces pruritic papules and vesicles 12–48 hours post-exposure. • Frequent offenders comprise nickel, cosmetics, and edibles. Biopsies reveal epidermal spongiosis accompanied by vesicle development and an inflammatory infiltrate, typically including eosinophils. Nummular dermatitis • Inflammatory dermatosis of indeterminate etiology. • Clinically presents as small papules and vesicles that merge into coin-shaped plaques. • Biopsies reveal epidermal spongiosis and inflammation in first lesions. Advanced lesions exhibit epidermal hyperplasia. Seborrheic dermatitis • Prevalent inflammatory dermatological condition impacting 1–3% of the population. Evidence indicates it may stem from an atypical immunological response to Malassezia organisms, though this remains contentious. • Clinically presents with erythematous, scaly papules and plaques, occasionally exhibiting a greasy look, located on the scalp, ears, eyebrows, and nasolabial region. Biopsies reveal varied epidermal spongiosis and hyperplasia accompanied by overlaying parakeratosis centered on hair follicles.  Pathology - Primary amyloidosis Definition: A plasma cell neoplasm characterized by the accumulation of AL amyloid in several tissues. Epidemiology • Uncommon ailment. The median age at diagnosis is 65 years, with a predominance of males. Aetiology The majority of patients possess an underlying plasma cell neoplasm yet do not fulfill the diagnostic criteria for plasma cell myeloma. Pathogenesis • AL amyloid consists of immunoglobulin light chains produced by monoclonal plasma cells, which aggregate in diverse tissues in a β-pleated sheet configuration. • The deposited amyloid comprises both intact light chains and fragments of the variable NH2-terminal region. Presentation • Clinical manifestations associated with amyloid accumulation in several organs. Commonly affected areas encompass the skin, kidneys, heart, liver, intestines, and peripheral nerves. Characteristic manifestations include purpura, peripheral neuropathy, cardiac insufficiency, nephrotic syndrome, and malabsorption. Histopathology • Amyloid can be identified in several tissues as a pink, amorphous material. The Congo Amyloid exhibits red staining under ordinary light microscopy and 'apple green' under polarized light. Bone marrow biopsies generally reveal a little elevation in plasma cells, which may present as either normal or abnormal. The plasma cells exhibit monotypism for either kappa or lambda light chains. Prognosis: • Dismal prognosis with a median survival of merely 2 years from diagnosis. The predominant cause of mortality is amyloid-related heart failure.  Pathology - Plasma cell myeloma Definition: A diffuse neoplasm of plasma cells originating from bone marrow, characterized by the presence of paraproteins in serum and/or urine. Epidemiology • Incidence ranges from 3 to 5 per 100,000 individuals. • Manifestations are observed in older persons, with a mean diagnostic age of 70 years. • There is a masculine predominance of 1.5:1. Aetiology • Unidentified. Pathogenesis The neoplastic plasma cells produce cytokines that activate osteoclasts, resulting in lytic bone lesions. Circulating paraprotein inhibits normal immunoglobulin synthesis, hence elevating the susceptibility to infections. Free light chains traversing the kidneys contribute to renal failure. Presentation: • Ostealgia and recurring infections. • Anemia, elevated ESR, hypercalcemia, and renal dysfunction are prevalent. Histopathology A definitive diagnosis necessitates a bone marrow biopsy. • The bone marrow exhibits an abundance of monoclonal plasma cells organized in clusters, nodules, or sheets. • Clonality can be confirmed immunohistochemically by demonstrating kappa or lambda light chain restriction. Prognosis • Myeloma is an incurable condition. • Average survival is 3–4 years post-diagnosis.  Pathology - Classical Hodgkin lymphoma A lymphoid tumor characterized by dysfunctional neoplastic B-cells, referred to as Hodgkin/Reed Sternberg (HRS) cells, situated amid a dense non-neoplastic inflammatory milieu. Epidemiology • Bimodal age distribution, characterized by a high incidence between 15 and 35 years, and a secondary peak in later life. • Males are predominantly affected, except in the case of the nodular sclerosis variation, which exhibits equal incidence across genders. Aetiology • Unknown; although, Epstein-Barr virus (EBV) infection has been associated with certain kinds. Presentation • The majority of patients have localized lymphadenopathy. • Fever, nocturnal diaphoresis, and weight loss are prevalent (referred to as 'B symptoms'). Histopathology • Lymph nodes are infiltrated by varying quantities of neoplastic HRS cells amid a robust inflammatory milieu The standard diagnosis The Reed-Sternberg cell is a substantial cell characterized by two prominent nuclei, each containing distinct eosinophilic nucleoli. Four histological subtypes are identified based on the quantity and characteristics of the HRS cells and the reactive background: nodular sclerosis, mixed cellularity, lymphocyte-rich, and lymphocyte-depleted. The immunophenotype of HRS cells is characterized by positivity for CD15 and negativity for CD30, exhibiting a distinctive membranous and Golgi staining pattern. PAX5 and MUM-1 are invariably positive in HRS cells, but CD20 and CD79a are typically negative or expressed at low levels. Prognosis: Contemporary treatment protocols provide a cure rate over 85% for classical Hodgkin lymphoma. Nodular lymphocyte-predominant Hodgkin lymphoma Nodular lymphocyte predominant Hodgkin lymphoma (NLPHL) is acknowledged as a unique subtype of Hodgkin lymphoma. NLPHL constitutes 75% of all Hodgkin lymphomas. It generally occurs in young to middle-aged adults between the ages of 30 and 50. The atypical B-cells, referred to as lymphocyte-predominant cells, are immunophenotypically differentiated from classical HRS cells; they generally do not express CD30 and CD15, while exhibiting significant expression of CD20 and EMA. The disease progresses slowly and is seldom lethal.  Pathology - Mantle cell lymphoma A mature B-cell neoplasm characterized by monomorphic, small to medium-sized lymphoid cells exhibiting uneven nuclear outlines and a CCND1 translocation. Epidemiology • Constitutes 3–10% of all non-Hodgkin B-cell lymphomas. • Primarily occurs in adults, with a mean age of 60 years. Aetiology: Unknown. Genetics • Nearly all instances exhibit a t(11;14) translocation involving the CCND1 (cyclin D1) and IGH genes. Deregulated expression of cyclin D1 leads to unrestrained proliferation of lymphoid cells. Presentation: The majority of individuals exhibit lymph node involvement. The liver, spleen, bone marrow, or peripheral blood may also be affected. Extranodal areas, especially the gastrointestinal tract, may also be involved. Histopathology • Affected tissues are substituted by sheets of monomorphic, tiny to medium-sized lymphoid cells exhibiting irregular nuclear contours. • Hyalinized small blood arteries and dispersed epithelioid histiocytes are frequently observed. Immunophenotype: B-cell markers PAX5, CD20, and CD79a exhibit positivity. • CD5 and cyclin D1 exhibit positivity. • CD23 and CD10 are often negative. Prognosis • Despite its unremarkable look, the prognosis is typically unfavorable, with a median survival of merely 3–5 years.  Pathology - Extranodal marginal zone lymphoma Definition: An extranodal mature B-cell neoplasm primarily consisting of tiny neoplastic marginal zone cells. Epidemiology • Constitutes 7–8% of all non-Hodgkin B-cell lymphomas. • Primarily occurs in adults with a mean age of 60. Locations of engagement • The gastrointestinal system constitutes 50% of all instances, with the stomach as the predominant site. • Additional locations encompass the lung, salivary gland, skin, thyroid, and breast. Etiology • Gastric instances are generally linked to Helicobacter pylori. • Additional implicated species comprise Campylobacter jejuni (jejunum) and Borrelia burgdorferi (skin). • Autoimmune illnesses are also linked, such as Hashimoto’s thyroiditis (thyroid) and Sjögren’s syndrome (salivary gland). Pathogenesis • The majority of cases are preceded by a chronic inflammatory condition that results in the accumulation of extranodal lymphoid tissue. • Extended stimulation of lymphoid proliferation ultimately culminates in the transition into a neoplastic process. Presentation • Symptoms associated with a mass at the affected location. Histopathology • Affected tissues comprise a diverse assemblage of small neoplastic B-cells that encircle and may infiltrate the underlying reactive lymphoid follicles. • The cellular composition includes marginal zone cells, monocytoid-like cells, small lymphocytes, and dispersed immunoblasts and centroblast-like cells. • In epithelial-lined tissues, the neoplastic lymphoid cells generally infiltrate and obliterate the epithelium, resulting in lymphoepithelial lesions. Immunophenotype: B-cell markers PAX5, CD20, and CD79a are expressed positively. CD5, CD10, CD23, and cyclin D1 are all absent. Prognosis: Exhibits indolent behavior with extended periods of disease-free remission post-treatment.  Pathology - Diffuse large B-cell lymphoma A mature B-cell neoplasm characterized by big B-lymphoid cells exhibiting a diffuse growth pattern. Epidemiology: Represents 25–30% of all non-Hodgkin lymphomas. • Primarily impacts senior individuals over the age of 60. Aetiology • Often unidentified in numerous instances. • Significant correlation with immunodeficiency conditions, including HIV or post-transplant scenarios, where the lymphoma is induced by EBV, HHV-8, or both. Genetics • Several genetic modifications have been identified in diffuse large B-cell lymphoma (DLBCL). The most prevalent translocation pertains to a segment of 3q that encodes the BCL6 gene. Presentation: A rapidly enlarging mass that may be nodal (60%) or extranodal (40%). The gastrointestinal system is the most prevalent extranodal site, however almost any location may be involved. Histopathology • Affected tissues are substituted by extensive sheets of giant atypical lymphoid cells, typically exceeding twice the size of a normal lymphocyte. • Apoptotic debris is commonly observed, and confluent regions of tumor necrosis may be present. Immunophenotype: Positive for B-cell markers PAX5, CD20, and CD79a. Cyclin D1 is absent. • Elevated proliferation index (typically 40–90% of cells). Prognosis: Survival rates have significantly improved with the introduction of the anti-CD20 inhibitor, rituximab, achieving long-term survival rates of approximately 60–75%. Bone marrow involvement is typically linked to a bad prognosis.  Pathology - Follicular lymphoma Definition: A mature B-cell neoplasm consisting of germinal center cells (centrocytes and centroblasts). Epidemiology • Represents approximately 20% of all non-Hodgkin lymphomas. • Primarily impacts individuals aged 50 to 60. Aetiology: Unknown. Genetics: 90% of cases exhibit a distinctive t(14;18) translocation, leading to the fusion of the BCL2 gene with the IGH locus. Deregulated synthesis of the anti-apoptotic Bcl-2 protein leads to clonal proliferation. Presentation: Extensive lymphadenopathy and splenomegaly. • Patients are often asymptomatic. Histopathology Nodal architecture is supplanted by contiguous neoplastic follicles. Neoplastic follicles are devoid of mantle zones and consist of haphazardly arranged neoplastic centroblasts and centrocytes. Tangible body macrophages are typically lacking. • Neoplastic cells typically exhibit interfollicular dissemination. Bone marrow involvement is defined by paratrabecular clusters of malignant centrocytes and centroblasts. Immunophenotype PAX5, CD20, and CD79a, which are B-cell markers, exhibit positivity. Bcl-2, Bcl-6, and CD10 are furthermore positive. • CD5, CD23, and cyclin D1 are absent. Prognosis is contingent upon the severity of the disease and the grade of the tumor. Approximately 25% progression into a high-grade lymphoma, typically diffuse large B-cell lymphoma, correlating with a swift clinical deterioration and mortality.  |
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