In Vivo Imaging of Miliaria Profunda Using High-Definition Optical Coherence Tomography: Diagnosis, Pathogenesis, and Treatment

Miliaria profunda (MP) is a condition of sweat duct obstruction manifesting with generalized papular eruption and anhidrosis.^1,2 Using imaging with high-definition optical coherence tomography (HD-OCT), we identified, in vivo, the depth of lesions in MP and the likely location of sweat duct obstruction. To our knowledge, this is the first time such an evaluation has been performed.

A man in his 30s presented with generalized anhidrosis for 5 months. When his body temperature was increased, “goose-bumps” appeared over his trunk and limbs, which resolved spontaneously within an hour of cooling. Findings of baseline skin imaging using HD-OCT (Skintell; Agfa Healthcare) were normal. However, after exercise testing extensive whitish papules appeared over his trunk and limbs (Figure 1). Starch-iodine testing revealed generalized anhidrosis.

Testing with intradermal carbachol, 0.01% at 1 mL (Miostat; Alcon Laboratories Inc), failed to stimulate sweat production in our patient, although it did stimulate sweat production in 5 age- and sex-matched controls. Visualization with HD-OCT was repeated at the previous locations after exercise testing, now with whitish papules present (Figure 2). Biopsy of a whitish papule revealed epidermal spongiosis and hyperkeratosis over the sweat orifice.

Aluminum hexachloride was applied to an age-, sex- and ethnicity-matched healthy volunteer’s chest, and serial HD-OCT images were taken daily. The aluminum salt was found in the sweat orifices in this healthy control, and underlying intraepidermal changes similar to the patient’s MP lesions developed.

Ultimately, isotretinoin, 10 mg 3 times per week, was prescribed for our patient. Three months later, a repeated exercise starch-iodine test revealed marked increased areas of sweating. Analysis of pixel color in pretreatment and posttreatment images revealed that hidrotic areas on the trunk (that were most important in lowering core body temperature) had increased from 8.4% to 92.6%.

A man in his 20s developed MP as he was recovering from widespread pityriasis rosea. His HD-OCT findings were very similar to those in case 1. He opted for conservative management.

The term miliaria profunda was coined to refer to the deeper level of sweat duct obstruction, at or below the dermoepidermal junction, in contrast to the superficial and deeper epidermis locations in miliaria crystallina and miliaria rubra, respectively.² This location of sweat duct obstruction in MP was determined experimentally in a healthy volunteer whose terminal sweat ducts were destroyed using electrolysis.²

Evaluation with HD-OCT in both of our patients localized the skin lesions to the epidermis. Dilated spiraling acrosyringium was identified, and the adjacent hyperrefractile (bright) substance likely represents macerated keratin (Figure 2), which can be correlated with the poorly demarcated whitish papules observed clinically and on dermoscopy. The lesions were also surrounded by a hyporefractile (dark) rim, which likely represents free fluid (water has a low refractive index) consequent to obstructed sweat outflow and correlating with the spongiosis observed in histologic analysis. This phenomenon was better observed via in vivo imaging than histologic analysis likely because of the dehydration process used in histologic slide preparation.

Aluminum hexachloride applied to a healthy volunteer to experimentally obstruct the sweat orifices produced HD-OCT changes similar to those seen in MP. In previous reports,^2-4 surface hyperkeratosis and parakeratosis of acrosyringium have been noted, but these were postulated to be only an epiphenomenon. We also identified these hyperkeratotic plugs in our histologic analysis, and by correlating histologic with HD-OCT findings, we determined that the obstruction most likely occurred at the sweat orifices due to these hyperkeratotic plugs. Such plugs can occur subsequent to inflammatory skin diseases⁵ such as pityriasis rosea (case 2). Patient 1 was treated with isotretinoin because retinoids are known to reduce hyperkeratinization.⁶ The marked response to isotretinoin in patient 1 further supports the important role of hyperkeratinization in the pathogenesis of MP.

Miliaria profunda can be effectively diagnosed using HD-OCT. Contrary to current belief, the evanescent skin papules are intraepidermal, and hyperkeratotic plugs at the sweat orifices are the likely cause of obstruction. We hereby propose that MP be renamed miliaria alba, following the pattern of the clinically descriptive names for miliaria crystallina and miliaria rubra.

Corresponding Author: Hong Liang Tey, MRCP, National Skin Centre, Singapore, 1 Mandalay Rd, Singapore 308205 (teyhongliang111@yahoo.com).

Published Online: November 12, 2014. doi:10.1001/jamadermatol.2014.3612.

Conflict of Interest Disclosures: None reported.

Additional Contributions: We thank Shunjie Chua, BEng, for his assistance in data collection.