Hyperpigmented papules and plaques on chest

Dx: Confluent and reticulated papillomatosis

Confluent and reticulated papillomatosis of Gougerot and Carteaud (CRP) is a rare skin disorder characterized by benign blue-gray or brown hyperpigmented hyperkeratotic papules and plaques. The lesions initially occur on the trunk or central chest as 1- to 2-mm warty papules that become confluent to form plaques, spreading to the neck, abdomen, and upper extremities. Peripherally, the lesions are distributed in a reticular pattern. Although less common, CRP may be isolated to one part of the body, including the face and genitals; the mucous membranes are swpared.

With the exception of Japan, where a male predominance is seen, young women are more commonly affected.¹ Patients are typically asymptomatic, or complain of mild pruritus and cosmetic concerns.

A disorder of keratinocyte maturation and differentiation?

The cause of CRP is unknown. Several theories have been entertained: an underlying endocrine disorder, a rare form of cutaneous amyloidosis, reaction to bacteria or fungus on the skin, and a keratinization abnormality.¹ Most patients with CRP do not have an underlying endocrine disorder or any evidence of amyloidosis, making these theories less likely. KOH preparation for fungal elements is typically negative and patients do not respond to antifungal therapy.

A bacterial cause has been implicated because CRP responds to antibiotics, but many have argued that antibiotics are acting as an anti-inflammatory agent rather than an antibacterial medication.¹ Others have suggested antibiotics may be acting to decrease epidermal proliferation by blocking protein and DNA synthesis and reducing keratinocyte production of cytokines.²

Overall, the most accepted theory is that it is a disorder of keratinocyte maturation and differentiation.^1,3 Histological analysis, electron microscopy (EM), and immunohistochemical studies support this theory. Hyperkeratosis can be seen on histological examination. On EM, the stratum granulosum contains more lamellar granules and a larger transition cell layer, and immunochemical analysis reveals an increased expression of genetic markers associated with keratinization.¹

The etiology of this keratinization abnormality is poorly understood.

CRP has been reported in several family members, prompting suggestions by some of a possible genetic component.⁴ Others have proposed staphylococcal enterotoxin B may promote certain immune factors causing abnormal keratinization.²

Is it CRP or tinea versicolor?

The differential for CRP includes:

• tinea or pityriasis versicolor
• tinea corporis
• seborrheic dermatitis
• keratosis follicularis (Darier disease)
• acanthosis nigricans
• macular amyloidosis.

Of all of these, however, CRP is most likely to be confused with tinea versicolor, as both are associated with hyper- or hypopigmented papules and plaques on the chest and back, as well as mild pruritus. In CRP, however, a Woods lamp and KOH will be negative, while with tinea versicolor, KOH will be positive and the Woods lamp may reveal yellow-green fluorescence.