Urticaria is a common skin disorder caused by localized mast cell degranulation, leading to itchy wheals that typically develop and fade within hours. Acute eczematous dermatitis presents as erythematous papules and plaques that can become crusted or scaled due to conditions like atopic dermatitis. Psoriasis is a chronic inflammatory disease characterized by well-demarcated salmon-colored plaques covered in silver scale. Lichen planus features purple, pruritic planar papules in a symmetric distribution. Common benign skin tumors include seborrheic keratoses, actinic keratoses, and melanocytic nevi, while squamous cell

1. COMMON DISEASES OF THE SKIN

2. ACUTE INFLAMMATORY DERMATOSES
• Acute dermatoses are often marked by
infiltrates consisting of mononuclear cells
rather than neutrophils
• Some acute lesions may persist, transitioning
to a chronic phase, while others are self-
limited.

5. Urticaria
• is a common disorder mediated by localized mast cell
degranulation, which leads to dermal microvascular
hyperpermeability.
• The resulting erythematous, edematous, and pruritic plaques are
termed wheals
• Pathogenesis - type 1 hypersensitivity reaction
• Sparse superficial perivenular infiltrate of mononuclear cells
• Superficial dermal edema causes splaying of collagen bundles
• Age- typically affects individuals between 20 and 40 years of age
• Individual lesions usually develop and fade within hours, but
episodes can persist for days or even months

6. Acute Eczematous Dermatitis
• New lesions take the form of erythematous papules, often with
overlying vesicles, which ooze and become crusted.
• Pruritus is characteristic.
• With persistence, these lesions coalesce into raised, scaling plaques
• “inside jobs” and “outside jobs”
• Allergic contact dermatitis, Atopic dermatitis, Drug-related
eczematous dermatitis, Photoeczematous dermatitis , Primary
irritant dermatitis
• Spongiosis characterizes all forms of acute eczematous dermatitis

8. Erythema Multiforme
• is characterized by epithelial injury mediated by skin-homing CD8+ cytotoxic T
lymphocytes.
• It is an uncommon, usually self-limited disorder that appears to be a
hypersensitivity response to certain infections and drugs
• The cytotoxic T cell attack is focused on the basal cells of cutaneous and mucosal
epithelia
• Present with a wide array of lesions, which may include macules, papules,
vesicles, and bullae
• Characteristic “targetoid” appearance
• Lymphocytes along the dermoepidermal junction
• With time confluent necrosis>>blister

10. Psoriasis
• is a common chronic inflammatory dermatosis
• is associated with an increased risk for heart attack and stroke
• Also associated in up to 10% of patients with arthritis
• Pathogenesis- T cell-mediated inflammatory disease, presumed to
be autoimmune in origin
– the antigens are not well described.
– Both genetic and environmental factors contribute to the risk.
– It is unclear whether the inciting antigens are self-antigens,
environmental antigens, or some combination of the two
– Sensitized populations of T cells home to the dermis, including CD4+
TH17 and TH1 cells and CD8+ T cells, and accumulate in the epidermis.
– These cells secrete cytokines and growth factors that induce
keratinocyte hyperproliferation
• Koebner phenomenon

11. • The typical lesion is a well-demarcated, pink to salmon–colored plaque
covered by loosely adherent silver-white scale.
• Acanthosis with regular downward elongation of the rete ridges(“test
tubes in a rack.”)
• loss of the stratum granulosum and extensive parakeratotic scale
• Thining of suprapapillary plates, and dilated and tortuous blood vessels
within the papillae >>Auspitz sign
• Neutrophils form small aggregates within both the spongiotic superficial
epidermis and the parakeratotic stratum corneum.
• Similar changes can be seen in superficial fungal infections
• most frequently affects the skin of the elbows,knees, scalp etc..
• In most cases psoriasis is limited in distribution

13. Lichen Planus
• The "6 Ps": purple, pruritic, planar , polygonal papules and plaques
• CD8+ T cell–mediated cytotoxic response against antigens in the
basal cell layer and the DEJ
• Sawtoothed rete ridges
• Interface dermatitis
• Wedge shaped hypergranulosis
• Civatte bodies (dyskeratotic keratinocytes)
• Wickham striae
• Lesions are multiple and are usually symmetrically distributed,
particularly on the extremities, and
• often occur around the wrists and elbows and on the vulva and
glans penis

15. Lichen simplex chronicus
• manifests as roughening of the skin
• It is a response to local repetitive trauma

16. Verrucae (Warts)
• are proliferative lesions of squamous
epithelial cells that are caused by HPV
• are most common in children and adolescents
• Different kinds on the basis of their gross
appearance and location

18. BLISTERING (BULLOUS) DISORDERS
Pemphigus (Vulgaris and Foliaceus)
Bullous Pemphigoid

22. TUMORS OF THE SKIN

23. Seborrheic Keratosis
• A common pigmented epidermal tumor
• occur most frequently in middle-age or older individuals.
• Arise spontaneously and are particularly numerous on the trunk
• are caused by acquired activating mutations in growth factor
signaling pathways
– FGFR3, PI3K/AKT pathway,RAS
• Are tan to dark brown round, exophytic, coinlike plaques that vary
in diameter
• Have a “stuck-on” appearance
• Leser-Trelat sign

25. Actinic keratosis
• Intraepidermal keratinocytic lesion secondary to solar
damage
• Most common precursor of cutaneous SCC
• Epidermal dysplasia that is not full thickness
• Parakeratosis, dermal solar elastosis and mild dermal
lymphocytic infiltrate
• Usually are less than 1 cm in diameter
• tan brown or red, and rough (sandpaper-like) to the touch
• rate of progression to SCC is small, varying from 0.1% to
2.6% per year

28. Squamous Cell Carcinoma

29. Basal Cell Carcinoma
• is a common slow-growing cancer
that rarely metastasizes.
• It tends to occur at sites subject to chronic sun exposure and in
lightly pigmented individuals
• The molecular hallmark is loss-of function mutations in PTCH1
• Manifest as pearly papules, often with prominent, dilated
subepidermal blood vessels
• multifocal superficial growths or nodular lesions
• Are not encountered on mucosal surfaces

31. Melanocytic Nevi
• refers to any benign congenital or acquired neoplasm of
melanocytes
• caused by somatic gain-of-function mutations in BRAF or RAS
• Are tan-to-brown, uniformly pigmented, small papules (5 mm or
less across) with well-defined, rounded borders
• Nuclei are uniform and round, and contain inconspicuous nucleoli
with little or no mitotic activity
• junctional nevi , compound nevi, intradermal nevi

33. Melanoma
• As with other cutaneous malignancies, melanoma is mainly
caused by UV light–induced DNA damage that leads to the
stepwise acquisition of driver mutations
• Intense intermittent exposure at an early age is particularly
harmful.
• Hereditary predisposition also plays a role in an estimated 5% to
10% of cases
• Often exhibit striking variations in pigmentation
• The borders are irregular and often “notched.”
• Microscopically, malignant cells grow as poorly formed nests or as
individual cells at all levels of the epidermis (pagetoid spread) and
in expansile dermal nodules

34. • Increasing thickness strongly correlates with
worse biologic behavior of melanomas (termed
Breslow thickness)
• Individual melanoma cells usually are
considerably larger than nevus cells.
• They have large nuclei with irregular contours,
chromatin that is characteristically clumped at
the periphery of the nuclear membrane, and
prominent “cherry red” eosinophilic nucleoli

37. The main clinical warning signs are as follows:
1. Rapid enlargement of a preexisting nevus
2. Itching or pain in a lesion
3. Development of a new pigmented lesion during
adult
life
4. Irregularity of the borders of a pigmented lesion
5. Variegation of color within a pigmented lesion
“ABCs” of melanoma: asymmetry, border, color,
diameter, and evolution (change of an existing nevus)

38. END