11 Miliaria Rubra

11 Miliaria Rubra (Prickly Heat)

CLINICAL APPLICATION QUESTIONS

A distraught 22-year-old mother presents her 9-month-old infant with a generalized papular eruption over the neck and upper torso. The child is irritable but otherwise alert and active. There are no other constitutional or systemic signs. You suspect miliaria.

1. What questions should you ask the mother to help you distinguish miliaria from a viral exanthem?

2. What physical examination features help you distinguish miliaria from a viral exanthem?

3. If you decide this infant has miliaria, what treatment measures can be taken?

4. If you decide this infant has miliaria, what should you tell the mother?

APPLICATION GUIDELINES

Onset

Three forms of miliaria occur, but only the common form will be discussed here.

Under favorable conditions, anyone can develop miliaria. Infants and young children, however, seem particularly prone to this eruption caused by sweat-duct occlusion. The onset may be gradual or sudden and usually suggests an acute viral exanthem. Infants become cranky and irritable, while those able to verbalize complain of an intense prick- ing discomfort rather than pruritus.

Evolution of Disease Process

Sheets of tightly grouped geometrically distributed irritable red papules develop;

these wax and wane in intensity depending on the ambient temperature and degree of activity. Because the sweat duct is temporarily blocked and the gland will continue to secrete, any sweat stimulus will cause a sudden apparent exacerbation. This can happen even after clinical resolution while the ducts are still recovering patency. In infants, cry- ing, emotional distress, and exertion associated with feeding frequently cause short- lived flares.

Evolution of Skin Lesions

Individual lesions may wax and wane but usually regress once the precipitating fac- tors are removed. An exception is when secondary infection supervenes. Then the lesions may become pustular or develop into a frank impetigo.

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From: Current Clinical Practice: Dermatology Skills for Primary Care: An Illustrated Guide D.J. Trozak, D.J. Tennenhouse, and J.J. Russell © Humana Press, Totowa, NJ

102 Part II / Papular, Papulosquamous, Papulo-Vesicular Lesions

Provoking Factors

An immature sweat gland apparatus in infants and individual genetic susceptibility play a role. Rapid change in ambient temperature, high humidity, occlusive clothing, fric- tion from garments, and any factor that favors skin surface bacterial colonization predis- poses to miliaria. A recent study implicates certain strains of S. epidermidis as the source of the polysaccharide plug that can be demonstrated microscopically in the eccrine duct orifice. Once occlusion has occurred, any stimulus that initiates sweating will cause a short-lived exacerbation.

Self-Medication

Self-treatment is not a problem in miliaria.

Supplemental Review From General History

Time of onset in relation to weather changes, heat stress, febrile illness, and other pro- voking factors will usually identify the reason for occurrence.

Dermatologic Physical Exam Primary Lesions

The earliest primary histologic lesion of miliaria is a crystalline intraepidermal vesi- cle (see Photo 38), which evolves into a small erythematous papule (see Photo 39). With prolonged occlusion, pustules may occur (see Photo 40).

Secondary Lesions

Secondary infection may lead to frank impetiginization.

Distribution

Microdistribution: Periporal (surrounds sweat duct orifices). Examination with a mag- nifier will demonstrate that the interspersed hair follicle openings are spared (see Fig. 10).

Macrodistribution: Large numbers of geometrically spaced tiny periporal papules arise symmetrically on covered areas of the trunk and in intertriginous regions. The face, arms, palms, and soles are spared.

Configuration

Grouped (tiny grouped geometrically spaced papules).

Indicated Supporting Diagnostic Data None.

Therapy

General Measures

Victims should avoid any circumstance that provokes sweating, as this will exacerbate symptoms and reactivate the eruption. High ambient temperatures, especially with high humidity or while in tight occlusive clothing, will prolong the glandular plugging. Clothing should be light, loose, and absorbent to wick moisture away from the skin surface.

Chapter 11 / Prickly Heat 103

Topical Therapy

The only measure ever shown to speed resolution of miliaria is epidermal lubrica- tion. Consider using a bland OTC lubricant that contains a modest concentration of urea and an α-hydroxy acid. Topically applied anhydrous lanolin has also been reported as beneficial. Recent data suggest that use of an antibacterial bath soap might be benefi- cial, and in refractory cases, intermittent use of a benzoyl peroxide wash or lotion may be helpful.

Systemic Therapy

Systemic antibiotics should be used where there is clear evidence of secondary infec- tion. They should be chosen on the basis of culture and sensitivity studies. These agents have no apparent effect on the primary process and are usually not required to treat pure miliaria. In the rare instance in which such therapy is considered for miliaria without sec- ondary infection, culture for sensitivity should be obtained from several duct orifice lesions. Initial therapy should be directed at the spectrum of sensitivity of S. epidermidis and the antibiotic should preferably be one that is readily delivered to both the sweat gland and skin surface.

Conditions That May Simulate Miliaria Viral Exanthems

Spring and summer viral illnesses may be confused with miliaria. These are usually of shorter duration and are associated with constitutional symptoms such as coryza, sore throat, fatigue, fever, or malaise. Cervical adenopathy is also common and is not seen with pure miliaria. Remember that miliaria can be a sequela of viral illness and both can have eruptions that may occur simultaneously or in sequence.

Figure 10: Microdistribution of miliaria.

104 Part II / Papular, Papulosquamous, Papulo-Vesicular Lesions

ANSWERS TO CLINICAL APPLICATION QUESTIONS

A distraught 22-year-old mother presents her 9-month-old infant with a generalized papular eruption over the neck and upper torso. The child is irritable but otherwise alert and active. There are no other constitutional or systemic signs. You suspect miliaria.

1. What questions should you ask the mother to help you distinguish mil- iaria from a viral exanthem?

Answer:

a. Has there been any recent heat stress (exposure to high ambient tempera- ture, high humidity, or tight or occlusive clothing)?

b. Has the child been exposed to anyone else with a known viral exanthem or illness?

c. Has the child been febrile or lethargic?

d. Is there a history of recent sore throat or upper respiratory symptoms?

e. Does the rash exacerbate with exposure to heat or with exertion (such as crying).

2. What physical examination features help you distinguish miliaria from a viral exanthem?

Answer: Oral findings such as an enanthem (mucous membrane rash) on the palate or mucous membranes is common with viral exanthems, but absent with miliaria. Regional adenopathy is common with viral exanthems, but absent with miliaria. Miliaria lesions are tiny red papules evenly spaced between hair follicles.

Viral exanthem papules are less evenly spaced.

3. If you decide this infant has miliaria, what treatment measures can be taken?

Answer: Keep the child’s environment cool and clothing light, and reduce exer- tion. Apply bland lubrication. On rare occasions, systemic antibiotics may be indi- cated for secondary infection.

4. If you decide this infant has miliaria, what should you tell the mother?

Answer: Miliaria is a benign self-limited condition that will eventually resolve.

Resolution of the sweat gland blockage may take several weeks, and during that time, any heat stress or exercise will cause an immediate and apparent flare of the eruption.