The Clinical Diversity of Atopic Dermatitis

Lesion Morphology

Although AD lesions often are described as pruritic erythematous papules and plaques, other common morphologies in SOC populations include prurigo nodules, lichenoid papules, perifollicular papules, nummular lesions, and psoriasiform lesions (Table). Instead of applying normative terms such as classic vs atypical to AD morphology, we urge clinicians to be familiar with the full spectrum of AD skin signs.

Prurigo Nodules—Prurigo nodules are hyperkeratotic or erosive nodules with severe pruritus, often grouped symmetrically on the extensor surfaces of the arms, legs, and trunk (Figure 1).^14,21 The skin between lesions usually is unaffected but can be dry or lichenified or display postinflammatory pigmentary changes.¹⁴ Prurigo nodules are common. In a study of a cohort of patients with prurigo nodularis (N=108), nearly half (46.3%) were determined to have either an atopic predisposition or underlying AD as a contributing cause of the lesions.²¹

FIGURE 1. Prurigo nodules on the leg of an Asian patient with atopic dermatitis.

Prurigo nodules as a phenotype of AD may be more common in certain SOC populations. Studies from SEA have reported a higher prevalence of prurigo nodules among patients with AD.²⁸ Although there are limited formal studies assessing the true prevalence of this lesion type in African American AD patients in the United States, clinical evidence supports more frequent appearance of prurigo nodules in non-White patients.²⁹ Contributing factors include suboptimal care for AD in SOC populations and/or barriers to health care access, resulting in more severe disease that increases the risk for this lesion type.¹⁴

Lichenoid Papules—Papular lichenoid lesions often present on the extensor surfaces of the arms and legs in AD (Figure 2).²² In a study of Nigerian patients with AD (N=1019), 54.1% had lichenoid papules.²⁴ A systematic review of AD characteristics by region similarly reported an increased prevalence of this lesion type in African studies.²⁸ Lichenoid variants of AD have been well described in SOC patients in the United States.²³ In contrast to the lesions of lichen planus, the lichenoid papules of AD usually are round, rarely display koebnerization, do not have Wickham striae, and predominantly are located on extensor surfaces.

FIGURE 2. Lichenoid papules on the hand of a Black patient with atopic dermatitis

Perifollicular Papules—Perifollicular accentuation—dermatitis enhanced around hair follicles—is a well-described lesional morphology of AD that is noted in all racial/ethnic groups (Figure 3).²² In fact, perifollicular accentuation is included as one of the Hanifin and Rajka minor criteria for AD.³⁰ Studies performed in Nigeria and India showed perifollicular accentuation in up to 70% of AD patients.^24,31 In a study of adult Thai patients (N=56), follicular lesions were found more frequently in intrinsic AD (29%) compared with extrinsic AD (12%).³²

FIGURE 3. Perifollicular papules on the back of a Black patient with atopic dermatitis.

Nummular and Psoriasiform Lesions—Nummular lesions may be red, oozing, excoriated, studded with pustules and/or present on the extensor extremities (Figure 4). In SOC patients, these lesions often occur in areas where hyperpigmentation is noted.²² Studies in the United States and Mexico demonstrated that 15% to 17% of AD patients displayed nummular lesions.^23,33 Similar to follicular papules, nummular lesions were linked to intrinsic AD in a study of adult Thai patients.³²

FIGURE 4. Nummular lesion on the arm of an Asian patient with atopic dermatitis.

Psoriasiform lesions show prominent scaling, lichenification, and clear demarcation.²⁵ It has been reported that the psoriasiform phenotype of AD is more common in Asian patients,²⁵ though this is likely an oversimplification. The participants in these studies were of Japanese and Korean ancestry, which covers a broad geographic region, and the grouping of individuals under a heterogeneous Asian category is unlikely to convey generalizable biologic or clinical information. Unsurprisingly, a systematic review of AD characteristics by region noted considerable phenotypical differences among patients in SEA, East Asia, Iran, and India.²⁸