Miliaria, also called sweat rash/heat rash/prickly heat is a skin disease marked by small and itchy rashes due to sweat trapped under the skin by clogged sweat gland ducts..
Aetiology
Main cause of miliaria is obstruction of the eccrine sweat glands or ducts. This can be due to cutaneous debris or bacteria such as Staphylococcus epidermidis with its formation of biofilms. The obstruction leads to leakage of sweat into the epidermis or dermis, resulting in cellular overhydration, swelling, and further occlusion of the ducts
- Occlusion of skin: Transdermal drug patches and tight clothing have been associated with miliaria
- Type I pseudohypoaldosteronism: Mineralocorticoid resistance resulting in loss of sodium through eccrine glands is associated with pustular miliaria rubra
- Strenuous physical activity
- Morvan syndrome: Rare autosomal recessive disease resulting in hyperhidrosis, among other abnormalities, which predisposes to miliaria
- Drugs that induce sweating: Bethanechol, clonidine, and neostigmine
Clinical features
Miliaria crystallina/sudamina (4.5-9% of neonates):
Ductal occlusion of the stratum corneum
Commonly affects neonates of ≤ 2 weeks age or adults who have recently relocated to a warmer climate.
- Superficial vesicles (1-2mm) resembling water droplets that easily rupture.
- Rash usually appears within a few days of exposure to risk factors and resolves within a day after the superficial layer of skin rubs off
- No inflammatory response (as lesion is superficial)
- Rash distribution: Upper trunk, neck, and head
Miliaria rubra (M/C form):
Ductal occlusion in the epidermis at the subcorneal layers
Seen in neonates at 1-3 weeks age. It can also affect up to 30% of adults living in hot and humid conditions.
- Inflammatory response present:
- Larger, erythematous papules and vesicles
- Pruritic and painful symptoms (symptoms during perspiration, causing more irritation)
- Rash distribution:
- Neonates: Groin, axilla, and neck
- Adults: Sites where clothes rub on skin such as trunk and extremities. Face usually spared.
Miliaria profunda (rarest form):
Ductal occlusion in the dermal-epidermal junction, specifically the papillary dermis.
Seen with recurrent episodes of miliaria rubra or individuals exposed to new warm climates such as military persons deployed in tropical climates.
- Firm, large, flesh-colored papules not centered around follicles(due to a deeper involvement of the skin at the dermal-epidermal junction)
- Eruption may vary with symptoms from extremely pruritic to asymptomatic. Skin rash usually appears within minutes-hours of perspiration and resolves within an hour of sweating cessation.
- Rash distribution: Trunk (mainly) >> arms & legs
Complications
Anhidrosis (:
M/serious complication leading to poor thermoregulation and heat exhaustion
May permanently disable a person from work or prevent an active person from continuing exercise or sports.
Bacterial superinfection:
- Miliaria pustulosa: Miliaria rubra + pustules (indicate bacterial superinfection)
- Periporitis staphylogenes: Superinfection with staphylococci causing impetigo or multiple abscesses
Differential diagnosis:
- Viral exanthems or viral infections such as herpes simplex or varicella
- Cutaneous candidiasis or other fungal skin infections
- Folliculitis, whether bacterial or pityrosporum
- Neonatal acne or erythema toxicum neonatorum
- Drug rashes, particularly acute, generalized, exanthematous pustulosis
- Grover disease
- Arthropod bites
- Lymphocytoma cutis or cutaneous T-cell pseudolymphomas
Management
General measures to decrease sweating, and eccrine duct blockage:
- Cooler environments
- Wearing breathable clothes
- Exfoliating the skin
- Removing skin occluding objects such as band-aids or patches
Miliaria crystallina:
Usually not treated as it is self-limited and usually resolves within 24 hours.
Miliaria rubra treatment:
Treatment is geared towards decreasing inflammation
- Mild-to-mid potency corticosteroids: Triamcinolone 0.1% cream (1-2 weeks)
- Miliaria pustulosa: Topical antibiotics (clindamycin)
Miliaria profunda:
- Combined oral isotretinoin 40 mg/day (2 months) + topical anhydrous lanolin