Collection of dermatological disorders

This article covers various dermatological disorders, including sebaceous and epidermoid cysts, cat scratch disease, cutaneous mastocytosis, miliaria, nummular eczema, angiokeratoma, dyshidrotic eczema, livedo reticularis, xeroderma pigmentosum, pseudofolliculitis barbae, and albinism.

• Description
  • Epidermoid cyst
    • Most common cutaneous cyst
    • Lined by stratified squamous epithelium and contains keratin
  • Sebaceous cyst
    • Formed by blockage of the sebaceous gland
    • Contains sebum
• Clinical features
  • Both
    • Slow-growing, mobile, firm, painless nodule
    • Localized predominantly on the face, head, neck, back, or genitals
    • Infection possible (causes painful, erythematous mass that may exude pus)
    • High probability of recurrence
  • Sebaceous cyst: dark-colored punctum may be seen
• Differential diagnosis: trichilemmal cyst (pilar cyst)
  • Description: a cyst that forms around a hair follicle
  • Clinical features
    • Similar to sebaceous cysts, but without a central excretory duct to the epidermis
    • Content is hard, firm, and odorless
  • Treatment: surgical excision
• Treatment
  • Asymptomatic cysts do not need treatment.
  • Intralesional steroids (triamcinolone) may help reduce inflammation.
  • In case of infection or pressure symptoms: total surgical excision
  • Oral antibiotics for infected cysts

References:^[1][2][3]

• Definition: : a benign, self-limiting infectious disease that is transmitted mainly by cats (via scratching, biting, or licking)
• Epidemiology: : predominantly affects children and adolescents
• Pathogen: : Bartonella henselae (gram negative, aerobic bacillus)
• Clinical features
  • General: malaise, loss of appetite, fever
  • Localized
    • One or more 5–10 mm large, erythematous, nontender cutaneous papules or vesicles develop approx. 3–10 days after exposure at the site of inoculation. ^[4]
    • Swollen, tender lymph nodes 7–60 days following exposure ; ^[4]
      • Develops as primary lesions disappear
      • Usually unilateral, occasionally suppurative
      • Most commonly involves lymph nodes of axillae, neck, or groin (nearest the site of inoculation)
      • Resolves after 2–4 months ^[4]
  • In immunocompromised individuals (e.g., patients with HIV)
    • Bacillary angiomatosis (red-purple papules that bleed easily)
    • Hepatic peliosis: a benign vascular condition characterized by multiple blood-filled cysts and vascular sinuses in the liver ^[5][6]
      • Can be asymptomatic or cause abdominal pain, jaundice, and/or liver failure
      • In rare cases, cysts may rupture, causing intraperitoneal hemorrhage
    • Bacteremia and endocarditis
• Diagnostics
  • Bacterial culture from blood, swabs, or lymph node aspirate
  • Antibody testing
  • Histological study
    • Warthin-Starry staining of the involved lymph node may show clusters of rod-shaped bacteria.
    • H&E staining of cutaneous lesions may show necrotizing granuloma formation and neutrophilic infiltrate.
• Differential diagnosis: Kaposi sarcoma (has lymphocytic infiltrate as opposed to bacillary angiomatosis)
• Treatment
  • Mild or moderate cases: azithromycin (5-day course) to decrease lymphadenopathy and the duration of illness
  • In the case of persistent and/or disseminated disease (e.g., bacillary angiomatosis): erythromycin OR doxycycline
  • In the case of CNS involvement or endocarditis: rifampicin PLUS either erythromycin OR doxycycline

^[7][8]

• Definition: a condition characterized by proliferation and accumulation of mast cells in the skin
• Epidemiology: mainly affects children
• Clinical features
  • Maculopapular cutaneous mastocytosis (MPCM)
    • Reddish-brown papules, macules, plaques, or nodules on the extremities, trunk, face, and scalp
    • Pruritis and skin flushing are common after exposure to triggers
  • Darier sign: localized erythema and urticaria following mechanical irritation (e.g., rubbing, scratching) of the skin or skin lesions that are rich in mast cells
  • Acute systemic anaphylactic reactions: abdominal pain, diarrhea, and syncope
  Diagnostics
  • Usually a clinical diagnosis
  • Laboratory studies (CBC, liver function tests, tryptase levels) to rule out systematic mastocytosis
  • Skin biopsy for definitive diagnosis
• Treatment: supportive treatment only (no curative treatment available)
  • Avoid triggers of mast cell degranulation
  • Antihistamines, mast-cell stabilizer (e.g., cromolyn)
  • Refractory cases: topical glucocorticoids, PUVA therapy
• Prognosis: resolve spontaneously before the onset of puberty ^[9]

• Definition: transient, papular exanthem following exposure to heat
• Etiology: blockage of the eccrine sweat ducts in hot and/or humid environments
• Localization: : mainly on the trunk, neck, and intertriginous areas
• Treatment
  • General measures to reduce sweating: wearing light, breathable fabrics, keeping the patient in a cool environment, removing occlusive bandages, etc.
  • Topical steroids; (hydrocortisone, triamcinolone), topical antibiotics for pustular eruptions (clindamycin, erythromycin)

• Description: chronic inflammatory skin condition; characterized by well-demarcated round lesions
• Etiology
  • Multifactorial
  • Primarily an immunological hypersensitivity reaction (dermatitis) due to xerosis and damage to the epidermal lipid barrier
• Clinical features
  • 2–5 cm large, coin-shaped, well-demarcated erythematous plaques
  • Pruritus, scabs
  • Primarily affects the extremities
• Differential diagnosis: For details, see “Overview of annular skin lesions.”
• Treatment
  • Symptomatic
    • Skin hydration with wet wraps and lotions
    • Oral antihistamines
  • Topical steroids and immune modulators (tacrolimus and pimecrolimus) to decrease inflammation

• Definition: maculopapular exanthem associated with viral infections, especially hepatitis B and Epstein-Barr virus (EBV)
• Epidemiology: age of onset is < 5 years ^[11]
• Clinical features
  • Affects the face, buttocks, and extensor surfaces of the extremities
  • Pruritus may occur
  • Self-limiting, lasting between 10 days and 6 months ^[12]
• Treatment: symptomatic

• Definition: benign ectasia of the superficial dermal blood vessels with characteristic hyperkeratosis of the papillary dermis
• Clinical features
  • Asymptomatic papules, plaques, or verrucous skin lesions
    • Red, blue, or black in color
    • Usually solitary (less commonly diffuse)
    • Most commonly located on the lower extremities and groin
  • Associated with Fabry disease: multiple skin lesions located on the trunk
• Diagnostics
  • Usually a clinical diagnosis
  • Skin biopsy: telangiectasia, acanthosis, hyperkeratosis
• Treatment: laser ablation, mainly a cosmetic procedure

• Definition: a condition characterized by a recurrent, acute blistering eczema of the palms and/or soles
• Etiology
  • Unknown (believed to be multifactorial)
  • Risk factors include:
    • Atopic dermatitis
    • Irritant contact dermatitis
    • Allergic contact dermatitis (e.g., nickel, cobalt, balsam of Peru, perfumes)
    • Dermatophyte infections
• Clinical features
  • Acute, recurrent episodes of pruritic vesicular/bullous eruptions on the palms, lateral aspects of the fingers, and/or soles
    • Warm weather exacerbates symptoms.
    • The lesions are usually multiple and deep-seated.
  • Severe cases include dystrophic nail changes (e.g., color changes, ridge formation)
• Diagnostics
  • Usually a clinical diagnosis.
  • Skin biopsy
    • To rule out differential diagnoses (e.g., psoriasis) or in case of poor response to treatment.
    • Findings include intraepidermal spongiotic vesicles/bullae without involvement of the eccrine sweat glands.
• Treatment
  • Avoid triggers (e.g., allergens and irritants such as metals, perfumes, or cigarette smoking)
  • Appropriate skin care (i.e., wash hands with lukewarm water and soap-free cleanser, apply emollients after drying hands adequately)
  • Topical corticosteroids for mild cases that do not respond to general measures
  • Oral corticosteroids for severe cases
  • Consider adding PUVA or UVA treatment for patients with refractory disease.
• Complications
  • Chronic hand dermatitis: lichenification, scaling, fissured patches and plaques
  • Secondary infection (e.g., Staphylococcus aureus)

• Description: reticular erythema with telangiectasias
• Etiology: paralysis of the deep vascular plexus of the skin caused due to chronic heat application (e.g., infrared radiation, hot water bottles)
• Pathophysiology: direct skin application of heat for extended periods of time → direct heat triggers increased melanin production → marbled, brownish hyperpigmentation
• Treatment ^[13]
  • Discontinue offending heat source
  • The condition usually resolves within months to years,
  • Permanent hyperpigmentation or scarring may occur: can be treated with topical tretinoin or hydroquinone
  • Topical 5-fluorouracil in the case of epithelial atypia
• Complications ^[13]
  • Squamous cell carcinoma
  • Merkel cell carcinoma: a rare, rapidly progressive neuroendocrine tumor that typically manifests as a painless, firm, nontender, red-blue nodule on the head or neck

• Callus: thick, toughened skin caused by repeated mechanical pressure and friction
• Clavus: a painful, hyperkeratotic lesion with a center core (corn) caused by frictional forces and trauma

• Definition: superficial bacterial skin infection with pit-like corneal defects on the soles of the feet accompanied by malodor and a burning sensation
• Epidemiology
  • Occurs worldwide (especially in athletes, industrial workers, and soldiers)
  • Risk factors include:
    • Hot, humid weather
    • Occlusive footwear
    • Hyperhidrosis
• Etiology
  • Caused by maceration and various bacteria
  • Most often occurs in association with insufficiently breathable footwear
• Clinical features: bilateral and multifocal cerebriform skin maceration and superficial erosions
• Treatment ^[14]
  • Regular changing of footwear and socks
  • Topical antibiotics (e.g., erythromycin, clindamycin)
  • Possibly botulinum toxin or iontophoresis to reduce local sweating

• Description: localized degeneration of subcutaneous adipose tissue
• Etiology: iatrogenic (secondary to subcutaneous injections), certain drugs (e.g., ARVT), pressure-induced, or idiopathic
• Treatment: depends on the underlying cause

• Description: chronic facial dermatitis affecting the perioral region
• Epidemiology: primarily children and women 20–45 years of age ^[15]
• Etiology
  • Unknown
  • Presumably caused by regular application of (glucocorticoid) creams and/or cosmetics
• Clinical features
  • Erythema with grouped papules and pustules
  • Dry skin with painful burning and a sensation of tightness
  • No residual scarring after resolution
• Treatment
  • Avoid using cosmetics or drugs containing corticosteroids.
  • In severe cases, local or systemic tetracycline

• Description: a rheumatological, spondylarthritic disease with simultaneous occurrence of synovitis, acne, pustulosis, hyperostosis, and osteitis
• Clinical features
  • Skin: acne, palmoplantar pustulosis
  • Musculoskeletal: synovitis, hyperostosis (particularly of the sternoclavicular joint, spine, and/or pelvis), and chronic recurrent osteitis
• Etiology: unknown
• Diagnostics
  • Mainly a clinical diagnosis
  • Imaging
    • X-ray: evidence of hyperostosis
    • Scintigraphy: enhancement in affected bones and joints
    • MRI: visible inflammatory reaction (osteitis)
• Treatment: primarily symptomatic

Livedo reticularis that does not regress after application of warmth is indicative of an underlying vascular disease and requires treatment.

• Description ^[17]
  • Rare, autosomal-recessive, hereditary skin disease caused by defective DNA repair mechanisms (i.e., nucleotide excision repair)
  • Minimal UV radiation has carcinogenic effects and can lead to severe skin damage in affected individuals,
• Epidemiology
  • Prevalence: 1:1,000,000 in the US
  • ♂ = ♀
• Clinical features
  • Cutaneous manifestations
    • Slow healing, blistering burns after minimal exposure to sunlight in 50% of affected individuals
    • Solar lentigos, xerosis, poikiloderma, telangiectasia due to repeated exposure to sunlight
    • Multiple precancerous lesions (actinic keratoses) develop during early childhood.
  • Ocular manifestations
    • Photophobia and dry eyes
    • Atrophy of eyelids, loss of eyelashes
    • Keratitis, corneal opacification, loss of vision
  • Progressive neurodegeneration (∼ 25% of cases): cognitive impairment, sensorineural hearing loss, ataxia, spasticity, decreased deep tendon reflexes
• Diagnosis
  • Primarily based on history and clinical findings
  • Confirmatory genetic testing
• Management
  • UV protection: limit exposure of skin and eyes to sunlight (e.g., protective clothing, high SPF sunscreen, UV-protective eyewear)
  • Vitamin D supplementation
  • Frequent skin cancer screening and ophthalmic exams
  • Systemic retinoids: non-melanoma skin cancer prophylaxis
• Complications
  • Skin cancer (basal cell carcinoma, squamous cell carcinoma, melanoma) at a young age (< 20 years)
  • Malignant tumors of the eyes and eyelids
• Prognosis: severely limited life expectancy ^[18][19]

• Description: inflammatory skin reaction in response to short hair that becomes entrapped within the skin
• Etiology
  • Usually occurs due to shaving (also known as razor bumps)
  • Most common in African American men because the hair shafts typically form tight coils
• Pathophysiology
  • Extrafollicular penetration: Hair enters the interfollicular epidermis after it exits the follicular orifice.
  • Transfollicular penetration: Hair penetrates the dermis before exiting the follicular orifice.
• Clinical features
  • Lesions: firm, hyperpigmented, tender, pruritic papules and pustules
  • Location: beard region (i.e., cheeks, jaw, and neck)
• Diagnostics: a clinical diagnosis
• Treatment
  • Cessation of shaving
  • Alternative hair-removal techniques (e.g., laser hair removal)
  • Adjunctive: topical treatments (e.g., retinoids, corticosteroids, antimicrobials)

• Definition: : congenital disorders of melanin synthesis resulting in hypopigmentation
  • Partial albinism: a genetic condition characterized by the partial absence of melanin pigment from melanosomes in the body due to defects in the biosynthesis of melanin
  • Total albinism: a genetic condition characterized by the total absence of melanin pigment from melanosomes in the body due to defects in the biosynthesis of melanin
• Epidemiology
  • Affects all races and both sexes
  • Most types of albinism are congenital and noticed early in life (e.g., newborns).
• Classification
  • Ocular albinism (OA): Only the visual system (e.g., iris, retina) is affected, but not the skin or hair.
  • Oculocutaneous albinism (OCA)
    • Absence of melanin in the skin, hair, and iris
    • May be associated with Chédiak-Higashi syndrome
• Pathophysiology: dysfunctional tyrosinase activity or impaired transport of tyrosine and/or melanin → decreased or absent melanin production (melanocyte levels are normal)
• Clinical features
  • Eyes
    • Translucent, hypopigmented blue, grey, or green irides
    • Photophobia, decreased visual acuity
    • Strabismus, nystagmus, amblyopia
    • Abnormalities of the optic nerve (e.g., hypoplasia, abnormal crossing of optic fibers at the optic chiasm)
  • Skin and hair: milky white color, photosensitivity, sunburns
  • Associated with increased risk of skin cancer
• Treatment: only supportive treatment, no curative treatment available
  • Treatment of strabismus: eye-patching , eye surgery
  • Avoidance of direct exposure to UV light and regular screening for skin cancer
  • Wearing (prescription) sunglasses
  • Nitisinone : used for the treatment of hereditary tyrosinemia type 1

• Definition: a congenital pigmentation disorder due to abnormal migration of melanocytes during embryogenesis
• Etiology: an autosomal dominant inherited disorder
• Clinical features
  • Patchy depigmentation of the hair and skin (e.g., poliosis)
  • Pale blue eyes or heterochromia iridum
  • Broad nasal root
  • Congenital hearing loss
  • Cleft lip and cleft palate
  • Neural tube defects
  • Associated with Hirschsprung disease
• Treatment: only supportive treatment, no curative treatment available

• Definition: a rare, very aggressive vascular malignancy, arising from endothelial cells of blood or lymphatic vessels ^[20]
• Epidemiology: peak incidence age > 70 years ^[20]
• Etiology ^[20]
  • Radiation (e.g., radiation therapy)
  • Chronic lymphedema: especially in postmastectomy lymph node resection
  • Chemicals: Vinyl chloride and arsenic are implicated in hepatic angiosarcoma.
• Clinical features ^[21][22]
  • Location
    • More common in sun-exposed areas
    • Usually occur on the head, neck, and breast
    • May involve the internal organs (e.g., hepatic angiosarcoma)
  • Lesion
    • Blue/purple-colored with a bruise-like appearance
    • Later stage: hemorrhage or ulceration
    • High variability in appearance
• Treatment ^[22]
  • Complete resection with wide margins
  • Resection may be complicated by the aggressive course of the disease and delayed diagnosis.

• Definition: skin reactions associated with the needle trauma caused by tattooing or the inks involved
• Types
  • Infection transmitted by needle or acquired after tattooing through damaged skin (e.g., impetigo, erysipelas)
  • Eczematous hypersensitivity reactions to tattoo ink (e.g., allergic contact dermatitis, photoallergic dermatitis)
  • New skin disease (e.g., psoriasis, eczema, vitiligo)
  • MRI burn due to tattoo ink containing metals (e.g., mercury, iron)
  • Skin cancer due to carcinogenic substances in tattooing ink
• Clinical features, diagnosis, and treatment: according to diagnosis and symptoms (e.g., antibiotic treatment of erysipelas)

• Definition: a condition of localized or generalized excessive sweating
• Epidemiology: estimated to affect ∼ 5% in the US ^[23]
• Etiology
  • Primary focal hyperhidrosis
  • Secondary hyperhidrosis (e.g., due to hyperthyroidism, malignancy, obesity, or adverse effects of medication)
• Clinical features: excessive sweating that interferes with activities of daily living, frequent skin infections (e.g., tinea pedis)
  • Primary focal hyperhidrosis
    • Usually localized (e.g., underarms, forehead)
    • Both sides of the body are affected.
    • No sweating during sleep; sweating begins immediately after waking up.
  • Secondary hyperhidrosis: generalized, may occur during sleep
• Diagnostics: clinical diagnosis, sweat test
• Treatment
  • Antiperspirants (over-the-counter or prescription)
  • Iontophoresis
  • Anticholinergics
  • Botulinum toxin injections
  • Surgery (surgical removal of sweat glands or sympathectomy)

• Definition: An iatrogenic skin lesion caused by accidental injection of a drug into an artery ^[24][26][27]
• Pathophysiology: embolic vessel occlusion and reflexive vasospasm → skin necrosis
• Symptoms
  • Local pain right after injection
  • Skin induration and reddening within hours following an injection
  • Purplish livedoid erythema with necrosis within days following an injection
• Treatment
  • No specific treatment exists.
  • In small lesions, conservative treatment with analgesics, topical antibiotics, and glucocorticoids can be used.
  • In extensive lesions, surgical debridement can be required.

• Definition: a benign and common condition of sebaceous glands manifesting as single or multiple soft, yellow papules
• Epidemiology
  • Adults > 40 years of age (most common in men)
  • Newborns
• Risk factors
  • Chronic immunosuppressive therapy (e.g., cyclosporine A)
  • Insulin, TSH, and hydrocortisone
  • HIV antiretroviral therapy
• Pathophysiology: ↓ androgen levels → ↓ sebocyte turnover → activation of sebocyte proliferation → sebaceous hyperplasia
• Clinical features: solitary nodule or multiple skin-colored or yellowish papules on the face (mainly forehead, cheeks, chin) and on the upper trunk
• Diagnostics
  • Dermoscopic examination: an aggregation of white to yellow sebaceous globules with surrounding crown vessels (cumulus sign) ^[29]
  • Biopsy: rule out basal cell carcinoma
• Differential diagnosis
  • Sebaceous adenoma
  • Basal cell carcinoma
  • Lupus miliaris disseminatus faciei
• Treatment: mainly for cosmetic reasons
  • Topical agents (e.g., trichloroacetic acid)
  • Systemic treatment (e.g., isotretinoin)
  • Instrumental procedures (e.g., cryotherapy, electrodesiccation, photodynamic, laser therapy)

Cutaneous granulomas are a group of conditions characterized by a chronic inflammatory skin response to a variety of stimuli, including metabolites, foreign bodies, and infection. They are classified as infectious or noninfectious. Diagnosis is primarily clinical For more information on the etiology, pathophysiology, and pathology of these conditions, see “Granulomatous inflammation.” ^[30]

Noninfectious cutaneous granulomas

Noninfectious cutaneous granulomas are often manifestations of systemic diseases, including diabetes, rheumatoid arthritis, and sarcoidosis.

Granuloma annulare

• Definition: a benign, palpable, ring-shaped nodule of unclear etiology that most commonly manifests on the extremities (especially the dorsal hands and feet)
• Epidemiology ^[31]
  • ♀ > ♂ (3:1)
  • Peak incidence: 55–60 years of age
• Classification ^[32]
  • Localized
  • Generalized (sparing the head, neck, palms, and soles)
• Clinical features
  • Varies from skin-colored to violaceous
  • Lesions may appear hypopigmented or hyperpigmented in darker skin tones.
  • Pruritus (associated with generalized granuloma annulare)
• Differential diagnosis: See “Overview of annular skin lesions” for details.
• Treatment
  • Localized disease typically resolves without treatment; treatment is recommended according to patient preferences for cosmetic reasons, in persistent pruritus, or if prognosis is uncertain.
  • Generalized granuloma annulare is more likely than localized lesions to require systemic therapy.
  • First-line: topical corticosteroids (e.g., clobetasol propionate)
  • Alternatives: intralesional corticosteroid injection (e.g., triamcinolone acetonide), calcineurin inhibitors (e.g., tacrolimus ointment), systemic steroid-sparing therapy (e.g., hydroxychloroquine, isotretinoin)
• Prognosis ^[33]
  • Localized: self-limiting
  • Generalized: chronic or relapsing

Necrobiosis lipoidica ^[34]

• Definition: a rare, chronic granulomatous disease of the skin associated with diabetes mellitus
• Epidemiology ^[35]
  • Approx. 60% of patients with necrobiosis lipoidica have diabetes mellitus.
  • ♀ > ♂
• Clinical features
  • Usually asymptomatic
  • Common sites: pretibial region
  • Initially, a reddish-brown papule that progresses to a yellow-brown papule or plaque with visible telangiectasias
  • Ulceration of the lesion may also occur following minor trauma
• Histopathology: necrobiotic palisading granuloma
  • Lymphohistiocytic infiltration with plasma cells, foam cells, and giant cells
  • Wall thickening and occlusion of small blood vessels
  • Destruction of collagen fibers in the entire corium
• Treatment: Corticosteroids may be effective (e.g., intralesional corticosteroid injections)

Rheumatoid nodules

• Definition: inflammatory cutaneous or subcutaneous lesions found primarily at pressure points (e.g., extensor side of the forearm, bony prominences)
• Epidemiology ^[35]
  • Most common extraarticular manifestation of rheumatoid arthritis (RA)
  • Associated with seropositive rheumatoid arthritis and more severe joint involvement than in individuals with no nodules ^[36]
• Clinical features: nontender, firm, subcutaneous nodules
• Histopathology: central necrosis with surrounding palisading histiocytes and granulomatous tissue ^[35]
• Treatment: intralesional corticosteroid injection or excision only required if the nodule causes pain or impairs movement
• For more information, see “Rheumatoid arthritis.”

Lupus pernio

• Definition: a pathognomonic manifestation of cutaneous sarcoidosis appearing as violaceous plaques on areas commonly exposed to cold (e.g., nose, cheeks, ears)
• Associations ^[30]
  • Sarcoidosis of the lungs (approx. 75%)
  • Sarcoidosis of the upper respiratory tract (approx. 50%)
• Clinical features
  • Extensive, indurated plaques that tend to scar
  • Distribution similar to the butterfly rash seen in systemic lupus erythematosus
• Treatment ^[37]
  • First-line: intralesional corticosteroid injection (e.g., triamcinolone acetonide)
  • Second-line: systemic glucocorticosteroids (e.g., prednisolone), steroid-sparing therapy (e.g., antimalarials, methotrexate, tetracycline)

Foreign body granulomas

• Definition: noncaseating granulomatous inflammation of the cutaneous or subcutaneous tissues in response to the introduction of foreign materials
• Classification ^[38]
  • Endogenous: due to endogenous material (e.g., hair fragments, cholesterol crystals, calcifications) identified by the immune system as foreign
  • Exogenous: due to introduction of exogenous material (e.g., cosmetic fillers, sutures, fish spines)
• Stages
  • Stage 1: formation of papule, nodule, or erythematous plaque
  • Stage 2: fibrosis and granuloma formation
• Diagnostics: ultrasound, biopsy ^[39]

Infectious cutaneous granulomas

• Definition: any granuloma caused by a pathogen
• Examples
  • Cutaneous tuberculosis: granulomatous inflammation with caseous necrosis caused by Mycobacterium tuberculosis
  • Tuberculoid leprosy: hyperesthetic, hairless, skin lesions caused by Mycobacterium leprae
  • Cutaneous leishmaniasis: the most common form of leishmaniasis, characterized by reddish macules and papules that may progress to ulcers

• Definition: a benign skin condition caused by the build-up of keratin around the hair follicles
• Epidemiology: : typically affects children or adolescents
• Etiology
  • Not fully understood ^[40]
  • Associated with atopic dermatitis and ichthyosis vulgaris
• Pathophysiology: increased keratinization → keratin plug formation at follicle orifices
• Clinical features
  • Asymptomatic lesions
  • Keratotic follicular papules; (the papules are hard, resulting in a rough skin texture)
  • Perifollicular erythema may be seen.
  • Most commonly located on the extensors of the proximal arms and thighs (less commonly on the face, trunk, buttocks, and distal extremities)
  • Exacerbation during the winter months and during pregnancy is common. ^[41][42]
• Diagnosis: clinical
• Treatment
  • Usually not required
  • In patients concerned about the appearance of lesions, temporary improvement can be achieved with:
    • Prevention of dry skin (e.g., using mild soaps and avoiding hot showers/baths)
    • Emollients and keratolytics containing, e.g., lactic acid or topical urea, to soften the skin
    • Topical retinoids: if treatment with emollients and keratolytics fails
    • Topical corticosteroids: in patients with severe inflammation
• Prognosis: benign condition ^[41]