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Miliaria
Evidence Levels: A Double-blind study B Clinical trial ≥ 20 subjects C Clinical trial < 20 subjects D Series ≥ 5 subjects E Anecdotal case reports
Miliaria is a benign, transient disorder caused by occlusion and resultant injury in the eccrine duct or, rarely, by a primary dysfunction of the eccrine duct. It is subdivided into miliaria crystallina, miliaria rubra, and miliaria profunda, based on the level of obliteration. Miliaria crystallina (sudamina), the most superficial form, occurs with occlusion of the sweat duct in the stratum corneum. It is self-limiting and typically appears as clear vesicles without significant erythema. Miliaria rubra (‘prickly heat’) is the most common, presenting as numerous pruritic non-follicular papules or vesicles with surrounding erythema. The obstruction occurs within the eccrine duct in the stratum malpighii. Typically, it occurs on the trunk, neck, or back but can affect other areas and has been reported to occur under splints, braces, and military uniforms because of the warm occlusive environment. It may also be rarely observed in cases of hypoaldosteronism and pseudohypoaldosteronism secondary to inflammation caused by elevated sodium chloride in sweat. Miliaria profunda is uncommon, classically occurring at the dermoepidermal junction or dermis; however, advances in imaging have begun to cause physicians to question this understanding, raising the possibility of acrosyringial involvement. Miliaria profunda is typically seen after repeated cases of miliaria rubra in tropical settings. These patients can also have associated systemic symptoms related to overheating.
Management Strategy
Miliaria most typically occurs as a result of excessive sweating in hot, humid conditions, with prolonged perspiration, or after an extended febrile illness. Sweat-inducing medications such as cholinergic agents, catecholamines, β-blockers, and opiates are linked to the development of miliaria. Few case reports suggest a potential association with anthracyclines, namely doxorubicin and idarubicin. There are less common reports of congenital miliaria in association with pseudohypoaldosteronism (PHA), hypothyroidism, and hypernatremia. In a few cases, miliaria crystallina has developed secondary to Stevens–Johnson syndrome/toxic epidermal necrolysis. Miliaria is often exacerbated by tight clothing and high humidity. Management begins with removal of the inciting factors . There is no strong evidence for the various treatment options.
Adults often develop miliaria during travel in the tropics, military service, or with heavy exercise. Gradual exposure helps to acclimatize to a hot and humid environment, but this may take a few months. Loose-fitting clothing , fans , and cool showers may minimize the symptoms. With the use of any topical lotion or cream, care must be taken to ensure that the product applied does not occlude the skin, further exacerbating the condition. In the case of severe itching, antihistamines, cold packs, and topical corticosteroids may be used. Oatmeal baths have been anecdotally reported to provide relief. However, all these measures will prove ineffective if the sweating is not reduced. All cases will respond to air conditioning, exposure of the involved skin, and the use of antipyretics in appropriate circumstances. Miliaria profunda has been reported to respond to oral retinoids and anhydrous lanolin.
Miliaria may be complicated by superinfection; it should be treated with systemic antibiotics or anti-yeast agents, aimed at staphylococci , or Candida sp. as the likely pathogens, respectively. Clinicians should make patients aware that anhidrosis in the area of the eruption may occur and persist for up to 3 weeks (or sometimes even longer) after the onset of lesions, and increased heat retention may occur if a large surface area was initially affected. Thus, patients at risk of heat exhaustion or heat stroke should take precautions to remain in air-conditioned environments during hot weather. A biopsy may be helpful in atypical cases of miliaria.
Specific Investigations
Nonneoplastic disorders of the eccrine glands
Wenzel FG, Horn TD. J Am Acad Dermatol 1998; 38: 1–7.
The histology and pathophysiology of eccrine sweat ducts are reviewed. The erythematous macule or papule of miliaria rubra occurs with an obstruction of the sweat duct at the stratum malpighii. In the case of miliaria crystallina, the disruption is in the stratum corneum and, with miliaria profunda, at or beneath the dermoepidermal junction. The pathogenesis of miliaria is reviewed, describing the role of resident bacteria and periodic acid–Schiff (PAS)-positive extracellular polysaccharide substance blocking eccrine ducts.
The role of extracellular polysaccharide substance produced by Staphylococcus epidermidis in miliaria
Mowad CM, McGinley KJ, Foglia A, et al. J Am Acad Dermatol 1995; 33: 729–33.
The ability of various strains of coagulase-negative staphylococci to induce miliaria under an occlusive dressing was evaluated. Staphylococcus epidermidis was the only strain that induced miliaria. The authors conclude that PAS-positive extracellular polysaccharide substance produced by S. epidermidis plays a central role in the pathogenesis of miliaria by obstructing sweat delivery.
Miliaria crystallina in an intensive care setting
Haas N, Martens F, Henz BM. Clin Exp Dermatol 2004; 29: 32–4.
Two cases of miliaria crystallina occurring in an intensive care setting are presented. The authors hypothesize that the mechanism is secondary to transient poral closure due to the drugs used in the intensive care setting that may have stimulated sweating.
Pruritus, papules and perspiration
LaShell M, Tankersley M, Guerra A. Ann Allergy Asthma Immunol 2007; 98: 299–302.
This article reviews common exercise-induced eruptions, with miliaria rubra being discussed as the cause of the patient’s recurring, self-limited eruption occurring with indoor exercise or hot tub exposure. An exercise challenge recreated the clinical picture and confirmed the diagnosis.
Miliaria-rash after neutropenic fever and induction chemotherapy for acute myelogenous leukemia
Nguyen TA, Stevens MP. An Bras Dermatol 2011; 86: 104–6.
A 40-year-old female developed miliaria crystallina after developing neutropenic fevers while on treatment with idarubicin and cytarabine. Treatment of the underlying fever led to resolution of cutaneous lesions. A review of miliaria and excessive perspiration associated with medications, including doxorubicin, bethanechol, salbutamol, and clonidine is discussed.
Pegylated liposomal doxorubicin-induced miliaria crystallina and lichenoid follicular eruption
Seghers AC, Tey HL, Tee SI, et al. Indian J Dermatol Venereol Leprol 2018; 84: 121.
A 24-year-old woman developed miliaria crystallina after the treatment of primary peritoneal carcinoma with pegylated liposomal doxorubicin. The authors propose that liposomal doxorubicin elimination via eccrine glands induced local necrosis and subsequent blockade of the acrosyringium in their patient.
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