Skin Pathology: Bacterial Infections

Impetigo: a contagious skin infection caused by Staphylococcus aureus or Streptococcus pyogenes, characterized by honey-colored crusts and bullae
- Can be further classified into:
  - Non-bullous impetigo: characterized by yellow-brown crusts and erosions
  - Bullous impetigo: characterized by large, fragile blisters
Cellulitis: a bacterial infection of the skin and subcutaneous tissues, often caused by Streptococcus pyogenes or Staphylococcus aureus
- Presents as erythema, swelling, and warmth of the skin
Erysipelas: a bacterial infection of the skin and mucous membranes, caused by Streptococcus pyogenes
- Characterized by a shiny, erythematous, and edematous plaque with a well-defined border

Herpes Simplex Virus (HSV): a viral infection that causes cold sores and fever blisters
- HSV-1: typically affects the face and lips
- HSV-2: typically affects the genitals and anogenital area
Human Papillomavirus (HPV): a viral infection that causes warts and papillomas
- Can be further classified into:
  - Common warts (Verruca vulgaris)
  - Plantar warts (Verruca plantaris)
  - Genital warts (Condyloma acuminatum)

Dermatophytosis: a fungal infection of the skin, hair, and nails, caused by species of Trichophyton, Microsporum, and Epidermophyton
- Can be further classified into:
  - Ringworm (Tinea corporis)
  - Athlete's foot (Tinea pedis)
  - Jock itch (Tinea cruris)
- Presents as annular, scaly plaques with a raised border

Scabies: a parasitic infection caused by Sarcoptes scabiei, characterized by intense pruritus and a polymorphic rash
- Presents as papules, vesicles, and burrows in a linear or sergiginous pattern
Pediculosis: a parasitic infection caused by lice, characterized by intense pruritus and a rash
- Can be further classified into:
  - Head lice (Pediculosis capitis)
  - Body lice (Pediculosis corporis)
  - Pubic lice (Pediculosis pubis)

Impetigo
- Caused by Staphylococcus aureus or Streptococcus pyogenes
- Characterized by honey-colored crusts and bullae
- Two types: non-bullous impetigo (yellow-brown crusts and erosions) and bullous impetigo (large, fragile blisters)
Cellulitis
- Bacterial infection of skin and subcutaneous tissues
- Often caused by Streptococcus pyogenes or Staphylococcus aureus
- Presents as erythema, swelling, and warmth of the skin
Erysipelas
- Bacterial infection of skin and mucous membranes
- Caused by Streptococcus pyogenes
- Characterized by a shiny, erythematous, and edematous plaque with a well-defined border

Herpes Simplex Virus (HSV)
- Causes cold sores and fever blisters
- Two types: HSV-1 (affects face and lips) and HSV-2 (affects genitals and anogenital area)
Human Papillomavirus (HPV)
- Causes warts and papillomas
- Three types: common warts (Verruca vulgaris), plantar warts (Verruca plantaris), and genital warts (Condyloma acuminatum)

Dermatophytosis
- Fungal infection of skin, hair, and nails
- Caused by Trichophyton, Microsporum, and Epidermophyton species
- Three types: ringworm (Tinea corporis), athlete's foot (Tinea pedis), and jock itch (Tinea cruris)
- Presents as annular, scaly plaques with a raised border

Scabies
- Caused by Sarcoptes scabiei
- Characterized by intense pruritus and a polymorphic rash
- Presents as papules, vesicles, and burrows in a linear or sergiginous pattern
Pediculosis
- Caused by lice
- Characterized by intense pruritus and a rash
- Three types: head lice (Pediculosis capitis), body lice (Pediculosis corporis), and pubic lice (Pediculosis pubis)

Melanoma develops from melanocytes, responsible for skin pigmentation
Accounts for 1% of skin cancer cases, but causes most skin cancer-related deaths
Four main subtypes:

Superficial Spreading Melanoma: most common (70% of cases)
Nodular Melanoma: 15-20% of cases, characterized by rapid growth and vertical invasion
Lentigo Maligna: 5-10% of cases, typically occurs on the face and grows slowly
Acral Lentiginous Melanoma: rare, occurring on palms, soles, and nail beds

Ultraviolet (UV) radiation: exposure increases melanoma risk, especially during childhood and adolescence
Genetic predisposition: family history of melanoma, especially in first-degree relatives
Fair skin: individuals with fair skin, light hair, and light eyes are more susceptible
Dysplastic nevi: presence of abnormal moles increases melanoma risk
Weakened immune system: individuals with compromised immune systems are more susceptible

ABCDE rule: diagnostic tool to identify melanoma:
- Asymmetry
- Border irregularity
- Color changes (multiple colors, especially black)
- Diameter > 6 mm
- Evolving (changes in size, shape, or color)
Lesion characteristics: melanoma lesions often appear as:
- Irregularly shaped or asymmetrical
- Multicolored or darkly pigmented
- Large (> 6 mm)
- Bleeding or crusting
- Itchy or painful

Dermatoscopy: non-invasive diagnostic tool to examine the skin
Biopsy: surgical procedure to remove a sample of the lesion for histopathological examination
Surgical excision: primary treatment, involving removal of the lesion and surrounding tissue
Adjuvant therapy: may include chemotherapy, radiation therapy, or immunotherapy for metastatic melanoma