Miliaria

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miliaria heat rash pathophysiology treatment

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Here is a comprehensive overview of miliaria drawn from authoritative dermatology textbooks.

Miliaria (Heat Rash)

Definition & Pathophysiology

Miliaria is a common disorder of the eccrine sweat glands caused by obstruction of eccrine sweat ducts, leading to retention of sweat within the skin. It occurs in conditions of increased heat and humidity - hot/humid climates, tropical regions, and in neonates who are over-swaddled or febrile.

Key mechanism: Staphylococcus epidermidis produces an extracellular polysaccharide substance that obstructs the eccrine duct orifice. The blocked sweat then ruptures into adjacent tissue at varying depths, producing different clinical variants. This does not, however, explain all cases (particularly congenital forms).

Affects up to 15% of newborns and is common across all ages in warm climates.

Classification by Level of Ductal Obstruction

The level at which sweat escapes into the skin determines the clinical type:

Type	Level of Obstruction	Morphology	Symptoms
Miliaria Crystallina	Stratum corneum (intracorneal/subcorneal)	Small (1 mm), clear, fragile, superficial vesicles ("dew drops"); no inflammation	Asymptomatic; ruptures at slightest trauma
Miliaria Rubra (Prickly Heat)	Prickle cell layer (epidermis)	1-3 mm discrete, erythematous papulovesicles on a bed of erythema	Intensely pruritic; prickling, burning, tingling sensation
Miliaria Pustulosa	Epidermis (preceded by duct injury)	Distinct, superficial, non-follicular sterile pustules	Pruritic; occurs in intertriginous and flexural areas
Miliaria Profunda	Dermal-epidermal junction (upper dermis)	1-3 mm asymptomatic, flesh-colored/whitish papules	Non-pruritic; lasts only ~1 hour after overheating ends

Clinical Features by Type

Miliaria Crystallina

Seen in bedridden patients with fever, over-bundled infants, or patients with hypernatremia
Drugs that can induce it: isotretinoin, adrenergic/cholinergic drugs, doxorubicin
Self-limited; no treatment required

Miliaria Rubra (Prickly Heat) - Most Common

Miliaria rubra: discrete erythematous papulovesicles on the trunk

Miliaria rubra - discrete erythematous papulovesicles (Andrews' Diseases of the Skin)

Predilection sites: antecubital and popliteal fossae, trunk, inframammary areas, abdomen (waistline), inguinal regions
Sites become macerated because evaporation of moisture is impeded
Can cause exercise-induced itching and may mimic or complicate atopic dermatitis
Histology: intraepidermal spongiosis + vesicles with chronic dermal inflammatory infiltrate

Miliaria Pustulosa

Preceded by another dermatitis that injures or blocks the sweat duct
Pustules are independent of hair follicles
Sites: intertriginous areas, flexural surfaces, scrotum, back (bedridden patients)
Associated with: contact dermatitis, lichen simplex chronicus, intertrigo
Recurrent episodes can be a sign of type I pseudohyperaldosteronism (salt-losing crises may precipitate it)

Miliaria Profunda

Rare; seen almost exclusively in the tropics
Usually follows a severe bout of miliaria rubra
Except for face, axillae, hands, and feet (which show compensatory hyperhidrosis), all sweat glands are nonfunctional
Concentrated on the trunk and extremities

Complications

Postmiliarial Hypohidrosis

Follows miliaria invariably; duration/severity proportional to the severity of miliaria
Sweating may be depressed to half the normal amount for up to 3 weeks
Symptoms: decreasing efficiency, irritability, anorexia, drowsiness, vertigo, headache

Tropical Anhidrotic Asthenia

Rare form with long-lasting poral occlusion producing anhidrosis and heat retention

Histology Summary

Miliaria crystallina: Intracorneal or subcorneal vesicle centered on the acrosyringium; little inflammation
Miliaria rubra: Intraepidermal spongiosis + vesicles; chronic inflammatory infiltrate in the dermis
Miliaria profunda: Perieccrine lymphocytic infiltration of sweat gland secretory coils (anhidrotic skin)

Treatment

The most effective treatment is removing the patient from the heat:

Cooling the environment - even a single night in air-conditioning significantly relieves symptoms
Circulating air fans to cool the skin
Anhydrous lanolin - resolves poral occlusion; helps restore normal sweat secretion; particularly effective in miliaria profunda
Hydrophilic ointment - dissolves keratinous plugs
Soothing/cooling baths with colloidal oatmeal or cornstarch (in moderation)
Dusting powders (cornstarch, baby talcum powder) for mild cases
Miliaria crystallina requires no treatment (self-limited)
Treat any underlying febrile illness; remove occlusive clothing

Special Populations

Neonates:

Miliaria crystallina may be present at birth (congenital)
Miliaria rubra usually appears after the first week of life
Precipitants: excessive warming in incubators, over-swaddling, fever, occlusive dressings
Resolves spontaneously once inciting factors are addressed

Sources:

Andrews' Diseases of the Skin, Ch. 3
Dermatology 2-Volume Set (5e), Ch. 34
Fitzpatrick's Dermatology, Vol. 1-2, Ch. 81 & 103

scaling accompanied by intense itching, burning, or pain

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Here is a clinically organized breakdown of conditions that produce scaling accompanied by intense itching, burning, or pain, organized by the dominant symptom and setting.

Scaling with Itching, Burning, or Pain - Differential Diagnosis

The combination of scaling + one or more of these symptoms is a core dermatological presentation. The dominant symptom (itch vs. burn/pain vs. both), distribution, and morphology of the scale are the key discriminators.

1. Seborrheic Dermatitis

Dominant symptoms: itching + burning

Erythematous, greasy scaling patches and plaques on sebaceous gland-rich sites: scalp, nasolabial folds, eyebrows, postauricular areas, external auditory canals, sternal chest, upper back, intertriginous areas
Severity ranges from mild erythema and pruritus to severe oily/thick scale with burning or tingling sensation
Chronic, relapsing course; worsens in cold/dry weather
Strongly associated with HIV (prevalence up to 83%) and Parkinson disease
Pathogen link: Malassezia spp. (also called Pityrosporum)
May co-occur with Pityrosporum folliculitis and seborrheic blepharitis (eyelid scaling + irritation)

Treatment: Topical antifungals (ketoconazole shampoo/cream), topical corticosteroids for flares

2. Psoriasis

Dominant symptoms: pruritus (variable intensity), occasionally burning

Discrete plaques with adherent silvery-white (micaceous) scale at sites of predilection (elbows, knees, scalp, lumbosacral area)
The itch in psoriasis is variable - some patients report intense pruritus; others describe burning, especially in inverse/flexural psoriasis
Driven by Th17/IL-17/IL-23 axis; TNF-α plays a co-amplifying role
Nail involvement (pitting, onycholysis) and psoriatic arthritis are important co-features
Koebner phenomenon: lesions appear at sites of skin trauma

Treatment: Topical corticosteroids, vitamin D analogues, methotrexate, biologics (anti-TNF, anti-IL-17, anti-IL-23)

3. Contact Dermatitis - Irritant (ICD) vs. Allergic (ACD)

Dominant symptoms: ICD → burning, pain, stinging; ACD → pruritus

This is a key clinical discriminator from textbook dermatology sources:

"A more frequent complaint of burning, pain, and stinging with ICD, in contrast to pruritus in areas of allergic contact dermatitis" - Dermatology 2-Volume Set (5e)

Both produce erythema, scaling, and weeping/crusting
ICD: immediate onset, sharply demarcated, dose-dependent; caused by soaps, detergents, solvents, acids
ACD: delayed (Type IV hypersensitivity), spreads beyond contact zone, intense pruritus
Eczematous cheilitis (lip involvement): xerosis, scaling, erythema, fissuring + burning and pruritus

Treatment: Remove offending agent; topical corticosteroids; barrier creams; patch testing for ACD

4. Xerosis (Dry Skin / Asteatotic Eczema)

Dominant symptoms: itching + burning + pin-prick sensations

"The most common symptoms of xerosis are nonspecific pruritus, burning sensations, and a pin prick-like feeling. Physical examination reveals roughness, fine scaling, and loss of elasticity in the skin." - Fitzpatrick's Dermatology

Especially common in the elderly, hypothyroid patients, and in cold/dry environments
Fine, powdery scale; "cracked earth" pattern (eczema craquelé) in severe cases
Aggravated by over-bathing, harsh soaps, low humidity, diuretics

Treatment: Emollients, humectants (urea, lactic acid), lukewarm bathing

5. Tinea Corporis / Dermatophytosis

Dominant symptom: mild-to-moderate pruritus

Sharply demarcated, annular scaling plaques with active, raised, scaly borders and central clearing
Mildly erythematous; may be chronic with mild pruritus as the only symptom
Caused by Trichophyton, Microsporum, or Epidermophyton species
Tinea pedis (athlete's foot): interdigital maceration, scaling, and burning/stinging are prominent
Tinea cruris: inguinal scaling + marked pruritus and burning

Treatment: Topical azoles (clotrimazole, miconazole); oral terbinafine or itraconazole for extensive/resistant cases

6. Lichen Planus

Dominant symptoms: intense pruritus; erosive forms → pain and burning

Classic: violaceous, flat-topped (planar), polygonal papules with fine white lines on the surface (Wickham's striae); fine surface scale
Scalp LP (lichen planopilaris): early signs include itching, burning, diffuse hair loss, perifollicular erythema, and scaling - progression leads to irreversible cicatricial scarring
Oral/erosive LP: painful, burning ulcers of the buccal mucosa and tongue
Nail LP: thinning, longitudinal ridging, pterygium formation

Treatment: Potent topical corticosteroids; intralesional steroids; systemic retinoids or immunosuppressants for widespread disease

7. Pityriasis Rosea

Dominant symptoms: pruritus (variable)

Begins with a herald patch (single oval, salmon-colored, scaling plaque), followed 1-2 weeks later by a widespread eruption along skin cleavage lines ("Christmas tree" pattern on back)
Usually asymptomatic, but pruritus may be present
Differential from tinea: Tinea has central clearing and positive KOH; PR has a collarette of scale pointing inward; PR usually clears spontaneously in 6-8 weeks

8. Erythrasma

Dominant symptoms: itching and burning (especially in the groin)

Caused by Corynebacterium minutissimum
Reddish-brown, well-demarcated patches with fine, dry scaling in intertriginous areas (groin, axillae, toe webs)
"Lesions are asymptomatic except in the groin, where there may be some itching and burning" - Andrews' Diseases of the Skin
Coral-red fluorescence under Wood's lamp is diagnostic

Treatment: Topical or oral erythromycin; topical azoles

Summary Table

Condition	Scale Character	Dominant Symptom	Key Distribution
Seborrheic dermatitis	Greasy, yellow	Itch + burning	Scalp, face, folds
Psoriasis	Silvery, micaceous	Itch (variable)	Extensor surfaces, scalp
Irritant contact dermatitis	Fine, variable	Burning/pain > itch	Exposed/contact site
Allergic contact dermatitis	Fine, weeping	Itch > burning	Contact + spread
Xerosis	Fine, powdery	Itch + burning/prickling	Generalized, legs
Tinea corporis	Peripheral (annular)	Mild itch	Trunk, limbs
Tinea pedis/cruris	Interdigital/border	Burning + itch	Feet, groin
Lichen planus	Fine surface scale	Intense itch; erosive = pain	Wrists, scalp, mucosa
Pityriasis rosea	Collarette (inward)	Variable itch	Trunk (Christmas tree)
Erythrasma	Fine, dry	Itch + burning	Intertriginous

Key clinical pearl: The symptom quality helps narrow the differential - burning/pain points toward irritant or erosive causes (ICD, erosive LP, herpes zoster with post-inflammatory scaling), while dominant pruritus favors allergic, atopic, or fungal etiologies. Distribution and scale morphology (greasy vs. silvery vs. fine) are equally discriminating.

Sources: Fitzpatrick's Dermatology, Vol. 1-2; Andrews' Diseases of the Skin; Dermatology 2-Volume Set (5e)

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