Eccrine miliaria

 

Salient features

 

·       Sweat retention can be caused by obstruction of the eccrine duct at various level

 

·       Miliaria crystallina or sudamina (superficial ductal occlusion) – clear vesicles

 

·       Miliaria rubra or prickly heat (intermediate ductal occlusion) – erythematous papules or pustules

 

·       Miliaria profunda or mammillaria (deeper ductal occlusion) – white papules

 

·       Common in neonates (whose eccrine sweat ducts are not fully developed) and adults living in hot, humid climates

 

·       Resolves with relocation to a cool environment

 

 

Introduction 

 

Miliaria is a group of eccrine disorders that arises due to the occlusion or disruption of eccrine sweat ducts, resulting in a leakage of sweat into the epidermis (miliaria crystallina and miliaria rubra) or dermis (miliaria profunda).. Blockage results in retention of sweat within the duct, causing a sweat retention vesicle to form.

 

The three forms of miliaria – miliaria crystallina (sudamina), miliaria rubra (prickly heat) and miliaria profunda – each reflecting obstruction of sweat ducts at different levels, from the stratum corneum to the dermal–epidermal junction. In miliaria crystallina, the obstruction is very superficial, within the stratum corneum, and the vesicle is subcorneal, containing clear fluid. In miliaria rubra, the obstruction is in the intraepidermal part of the sweat duct, with leakage and then formation of a vesicle around the duct. In miliaria profunda, there is rupture of the duct at the level of or below the dermal–epidermal junction.

 

 

 

 

Epidemiology

Miliaria is most common in neonates whose eccrine ducts are not fully developed. It is also common in children and adults who live or work in very hot, humid environments.

 

Clinical features

 

Each type of miliaria is clinically distinctive.

 

Miliaria crystallina

Clear, thin‐walled superficial vesicles, 1–2 mm in diameter without an inflammatory areola, are usually symptomless and develop in crops. It is most commonly observed on the face and upper trunk of neonates and on the trunk in children and adults. The vesicles soon rupture, and are followed by superficial, branny desquamation.

 

Miliaria rubra

 

The most common and clinically important form is miliaria rubra. The lesions are uniformly small, non-follicular, erythematous macules and papules topped by a punctate vesicle, which may be present in very large numbers. Characteristically, the lesions produce intense discomfort in the form of an unbearable pricking sensation. Onset is within days to weeks of exposure to hot environments. Miliaria rubra may become pustular, especially in chronic, extensive cases. Miliaria pustulosa, as this variant is known, is sterile, although secondary bacterial infection may occur. Relief is often instantaneous when the stimulus to sweating is abolished by a cool shower. Miliaria rubra typically occurs on the neck and upper trunk in neonates and in both children and adults in hot climates. Extensive cases of miliaria rubra can lead to hyperpyrexia.

 

 

Miliaria profunda

 

This nearly always follows repeated attacks of miliaria rubra when occlusion may extend to a deeper level and produce miliaria profunda. Because of their deeper location, the sweat retention vesicles of miliaria profunda appear clinically as multiple discrete, pale, firm1 to 3 mm papules that resemble gooseflesh. They start within minutes of initiation of sweating and subside within 1 to 2 hours after the sweating ceases.Since the sweat retention vesicle lies in the upper dermis below the level of the itch receptors, lesions of miliaria profunda are asymptomatic. Only in those patients with concomitant miliaria rubra can pruritus or burning develop. Miliaria profunda is relatively rare and typically occurs on the trunk and proximal extremities in adults in hot climates.

 

 

THREE TYPES OF MILIARIA
Type	Location of obstruction	Cutaneous lesions	Patient population(s)	Most common locations
Crystallina	Stratum corneum	Non-pruritic, clear, fragile, 1 mm vesicles	Neonates <2 weeks of age Children and adults in hot climates	Face and trunk
Rubra	Mid-epidermis	Pruritic, erythematous, 1–3 mm papules; may have pustules (miliaria pustulosa)	Neonates 1–3 weeks of age Children and adults in hot climates	Neck and upper trunk
Profunda	Dermal–epidermal junction	Non-pruritic, white, 1–3 mm papules	Adults in hot climates; often with multiple bouts of miliaria rubra	Trunk and proximal extremities

 

 

 

Disease course and prognosis

 

This depends mainly on environmental factors. If continued sweating occurs, recurrent episodes lasting a few days are usual, but discomfort may be continuous. However, after a few months some degree of acclimatization occurs, and the disorder becomes less prevalent.

The most important complications of miliaria are secondary infection and disturbance of heat regulation. Secondary bacterial infection may present as impetigo. Miliaria rubra in young infants may predispose to multiple superimposed staphylococcal abscesses. When large numbers of sweat glands are occluded and essentially non-functional, these individuals are at risk for significant thermoregulatory problems and a compensatory hyperhidrosis of the face is routinely observed. Axillary and inguinal lymphadenopathy can also be seen, with resolution upon clearing of the miliaria. The term “tropical anhidrotic asthenia” has been applied to these patients.

 

Pathology

Biopsy specimens demonstrate ductal blockage. Obstruction of sweat ducts at the level appropriate for each type of miliaria is due to the formation of Keratinous plugs: in the stratum corneum for miliaria crystallina; the mid-epidermis or spinous layer for miliaria rubra; and at the dermal–epidermal junction for miliaria profunda. Sweat retention vesicles may be seen underlying the respective sites of occlusion. Dermal inflammation is absent in miliaria crystallina, whereas perivascular lymphocytic infiltrates and vasodilation are evident in miliaria rubra. An eosinophilic cast can be seen occluding sweat ducts at the dermal–epidermal junction or intraepidermally in miliaria profunda. Periductal infiltration of lymphocytes is also seen along with mild focal spongiosis of the adjacent epidermis. Special stains may reveal Gram-positive bacteria in both rubra and profunda lesions, but cultures are typically negative unless the lesions are secondarily infected.

 

Diagnosis

Each type of miliaria has such a classic clinical presentation that the diagnosis is usually apparent.

 

Treatment

 

The only really effective prevention or treatment for all types of miliaria is avoidance of further sweating. This can be achieved by placing the patient in a cool environment, in which sweating stops, for several days to weeks. Gradually, the obstructed sweat ducts shed their occluding keratinous plugs and normal sweating is restored. Even if this is achieved only for a few hours a day, as in an air‐conditioned office or bedroom, considerable relief is experienced. For the very susceptible person, a move away from tropical climates may be essential. Avoidance of excessive clothing, friction from clothing, excessive use of soap and contact of the skin with irritants will reduce the incidence. The large number of treatments advocated for prickly heat is the best indication of their relative ineffectiveness if sweating is not reduced. In the absence of gross secondary sepsis, the effect of topical or systemic antibiotics or other antibacterial preparations on established miliaria is disappointing, but they may have some role in prophylaxis. Oral ascorbic acid 500 mg twice daily is found to diminish the severity of miliaria, as is the degree of subsequent anhidrosis. Calamine lotion is probably as effective as anything for the relief of discomfort, but because of its drying effect, a bland emollient (e.g. oily cream or menthol in aqueous cream) may subsequently be required to prevent further epidermal damage.

 

Therapeutic ladder

First line

·        Control local environment (remove excess bedding, fans, air conditioning)

·        Cool the skin (damp compresses, cool showers)

·        Avoid tight or excessive clothing

Second line

·        Menthol (e.g. 0.5% menthol in aqueous cream)

·        Topical antibiotics if there is secondary infection

·        Mild topical steroids

Third line

·        Removal to cooler climate

·        Prophylactic oral vitamin C