Vesicular eruption 
in an ICU patient

HOW TO TAKE THE POST-TEST: This Clinical Advisor CME activity consists of 3 articles. To obtain credit, you must also read Brown macules on a depigmented skin patch and Oral hyperpigmentation. Then take the post-test here.Miliaria crystallina, the mildest form...

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HOW TO TAKE THE POST-TEST: This Clinical Advisor CME activity consists of 3 articles. To obtain credit, you must also read Brown macules on a depigmented skin patch and Oral hyperpigmentation. Then take the post-test here.

Miliaria crystallina, the mildest form of so-called heat rash, is one of three variants of miliaria. All three variants—miliaria crystallina, miliaria rubra, and miliaria profunda—occur due to obstruction of eccrine sweat glands, most frequently resulting from increased temperature, either exogenous or endogenous. Miliaria has a propensity to occur on the forehead, neck, upper trunk, and any occluded areas. 

Classically, miliaria occurs in children in warm climates, particularly in the newborn period.^1-3 More specifically, miliaria cystallina often present at birth, and its etiology is explained by obstruction of the eccrine sweat duct at the level of the stratum corneum. Its superficial involvement of the epidermis results in the clinical presentation of clear, “dewdrop”-like vesicles in the absence of erythema.¹ 

In contrast, miliaria rubra, often referred to as “prickly heat,” is caused by occlusion of eccrine sweat glands at the level of the mid-epidermis, resulting in pruritic, red papules of 1 mm to 3 mm on the neck and upper trunk. The involved sweat ducts rupture and leak sweat into surrounding tissues, inducing an inflammatory response.^1,2 

Of note, there is a variant of miliaria rubra called miliaria pustulosa, which is usually sterile on cultures but can become secondarily infected with bacteria. An even rarer variant of miliaria known as miliaria profunda involves the dermal-epidermal junction and presents as non-pruritic white papules of 1 mm to 3 mm on the trunk and proximal extremities. This variant is found more commonly in adults in hot climates, often in coexistence with miliaria rubra.¹ 

Miliaria is a common condition, particularly among newborns in warm climates. Both miliaria crystallina and miliaria rubra are observed in up to 15% of newborns, typically in the setting of excessive warming inside an incubator, overswaddling, fever, or occlusive dressings.¹ Miliaria crystallina presents as nonpruritic clear, fragile, 1-mm vesicles.

Although the classic patient population consists of neonates younger than age two weeks, miliaria crystallina also can occur among persons in ICUs who are intubated and sedated for many weeks. Often these patients have such endogenous factors as high fevers and such exogenous factors as warm rooms and occlusion with blankets and clothing that contribute to eccrine duct obstruction.

Miliaria crystallina is associated with no racial or sex predisposition. Despite the fact that miliaria crystallina also is not associated with any underlying systemic disease, instituting treatment in these patients is still important when large numbers of sweat glands become occluded and nonfunctional, as these patients may lose the ability for thermoregulation, leading to a compensatory hyperhidrosis of the face. These patients may also exhibit axillary and inguinal lymphadenopathy that will resolve with resolution of the miliaria.^1,2 

Diagnosis of miliaria crystallina, as with the other miliaria variants, usually is quite apparent due to its classic clinical presentation. The superficial-appearing clear vesicles are quite unique to miliaria crystallina. Puncturing a vesicle with a fine needle—an easy and simple diagnostic test—releases trapped clear sweat. A biopsy is neither necessary nor recommended. 

On pathology, the specimen should demonstrate ductal blockage at the appropriate level, the stratum corneum.¹ There typically is no dermal inflammation in miliaria crystallina. While the diagnosis for miliaria crystallina is very unique, the diagnosis for miliaria rubra may be less straightforward. Differential diagnosis in neonates would include erythema toxicum neonatorum, neonatal cephalic pustulosis, candidiasis, and in atypical and rarer cases, other vesiculopustular diseases of the newborn. 

The differential diagnosis for adults includes folliculitis, candidiasis, and Grover’s disease.¹ If a biopsy of miliaria rubra is performed, histology will show sweat duct occlusion at the mid-epidermis or spinous layer with perivascular lymphocytic infiltrates and vasodilation. An eosinophilic cast may be seen in miliaria profunda with occlusion at the deepest level, the dermal-epidermal junction.^1,2 

As with the other miliaria variants, treatment for miliaria crystallina involves placing the patient in a cool environment—as we recommended for our patient—to decrease sweating. Using a fan and ice packs, avoiding occlusion and heavy blankets, and treating high fevers will resolve the miliaria. Eventually, the obstructed eccrine ducts will shed their occluding keratinous plug, and the patient should sweat normally.

The vesicles in miliaria crystallina should resolve very quickly, within approximately one week. Usually, no other treatments are necessary. Keeping the patient from overheating is the mainstay of prevention.^1,2

Topical medication such as corticosteroids, antibiotics, and retinoids have been advocated but typically are not recommended for miliaria crystallina. However, these agents may provide symptomatic relief for patients with miliaria rubra and miliaria profunda. Anhydrous lanolin and istotretinoin also have been reported as effective treatments for miliaria profunda.^1,2 

Tiffany L. Shih, MD, is a resident physician at the University of Minnesota in Minneapolis.

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HOW TO TAKE THE POST-TEST: This Clinical Advisor CME activity consists of 3 articles. To obtain credit, you must also read Brown macules on a depigmented skin patch and Oral hyperpigmentation. Then take the post-test here.