Miliaria

1 - DIAGNOSIS

Miliaria is sweat retention due to obstruction of the sweat ducts. Depending on the level at which obstruction occurs in the sweat glands, miliaria is classified as miliara crystalline, miliara rubra or miliara profunda.

1.1 - MILIARIA CRYSTALLINE

It occurs during acute febrile illnesses with sudden sweating but can also be observed with classic sunburn. It presents as an asymptomatic outbreak of multiple superficial vesicular lesions with a clear content that look like dewdrops on the healthy skin of the trunk and abdomen, but also on the face in children. The obstruction is in the stratum corneum. Miliaria crystalline heals spontaneously within a few hours giving rise to a branny desquamation.

1.2 - MILIARIA RUBRA

It is the classic prickly heat, which occurs during prolonged exposure to hot, wet or dry climates in the presence of predisposing factors (Table I). The rash is made up of non-follicular papular and papulovesicular lesions that are uniform in size, 1 to 2 mm in diameter, bright red and associated with an inflammatory reaction. The condition is associated with itching and a burning sensation of varying intensity. The lesions may occur all over the body, but are most frequently observed on the sides of the trunk, on the back, the neck and in areas of friction (large folds...). In children and women using occlusive cosmetics, very profuse lesions are often seen on the face. Occasionally, the vesicles become pustular and are then called miliaria pustulosa (amicrobic lesions). If the bad conditions persist, the rash can become lichenoid, with papular curved lesions. Complications may occur at any time (Table II). The simple forms are characterised by pruritic, erythematous and desquamative areas evocative due to their location and exacerbation by heat. Obstruction occurs within the Malpighian layer. If conditions improve, the disease clears giving rise to a characteristic branny desquamation. This healing is followed by a hypohidrosis of the affected areas for two to three weeks, exposing patients to relapse.

1.3 - MILIARIA PROFUNDA

It is a rare condition occurring after repeated episodes of miliaria rubra and observed primarily in the tropics. The rash is asymptomatic and consists of papules 1 to 3 mm in diameter on the trunk, but also on the extremities unlike the other forms of miliaria. The skin is generally dry. The obstruction occurs below the dermo-epidermal junction. Miliaria profunda is associated with axillary and inguinal lymphadenopathy and compensatory facial and axillary hyperhidrosis. These patients may develop tropical anhydrotic asthenia, which is the final stage of this major disorder of sweat secretion. It is characterized by general and functional signs such as asthenia, malaise, vomiting, faintness and tachycardia. The general signs are often in the forefront, leading to diagnostic errors. The symptoms may lead to malignant hyperthermia that can cause death if exposure persists.

2 - PATHOPHYSIOLOGY

The exact etiopathogenesis of miliaria is unclear. The obstruction of the sweat duct is due to PAS-positive material with or without a parakeratotic cap. The exact origin of the two elements is uncertain. The first cause is, according to studies, hyperhydration of the stratum corneum by sweat with a high sodium content, delipidation of the keratinocytes around the sweat pores or injury to the luminal cells by cocci, especially Staphylococcus epidermis. There is also a genetic predisposition. The disease is probably caused by numerous factors.

3 - TREATMENT

3.1 - AIMS

The goals of treatment are to reduce or stop sweat secretion, to allow and accelerate the evaporation of the already secreted sweat, to prevent and treat complications and relapses and, finally, to promote desquamation.

3.2 - MEASURES

The measure consisting in changing the temperature and humidity of the environment of the patient is the only truly radical measures. Many means are used empirically. General measures are primarily based on the use of air conditioning or ceiling fans a few hours per day or continuously. Ascorbic acid (1 g/d), anhydrous lanolin, antiseptics, topical and/or systemic antibiotics, inert or antiseptic powders, keratolytics, and topical retinoids may all be used in this indication. The literature contains very little information on these very common tropical disorders. Obviously, no controlled trial is available. Antihistamines used systemically or soothing lotions can reduce the functional signs. In severe cases giving rise to heat intolerance, only a change in environment can lead to healing.

3.3 - INDICATIONS

Miliria crystalline heals spontaneously; all unnecessary topical treatment should be avoided.

In miliria rubra, no specific treatment is required for the localised and uncomplicated forms. It is recommended to remove the favouring factors, including occlusive cosmetics, and to prescribe antiseptics. In the uncomplicated widespread forms, air conditioning and/or ceiling fans are useful. Antiseptics and, optionally, inert powders may be also be used. It is in this indication that ascorbic acid (1 g/d) is sometimes recommended. In patients presenting major functional signs, systemic antihistamine therapy and emollient bath products may be prescribed. In the event of secondary infection, an antibiotic active against the main skin germs should also be used (macrolides or penicillin M). In the event of onset of eczema, topical treatments should be discontinued and a short course of corticosteroids prescribed.

In miliria profunda, the same measures are useful. In the absence of improvement after 2 to 3 weeks, a change of environment should be considered. Lanolin applied to the lesions combined with oral isotretinoin has been recommended, but the validity of this treatment regimen has not been confirmed.