PMC7234341_01
(a) Clinical photograph. Hyperpigmented papules coalescing into plaques surrounded by distinctive keratotic ridges may be appreciated in a linear distribution on the right upper extremity and shoulder. (b) Clinical photograph. Keratotic ridges with central grooves are evident on closer examination.
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The lesions appeared to follow lines of Blaschko, with progression to the shoulder and mid-scapula during 5 months of observation (Figure 1(a) and (b)).
Hematoxylin and eosin stain, original magnification. Keratin-filled epidermal invaginations with angulated, parakeratotic tiers (cornoid lamellae) can be appreciated.
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A skin biopsy revealed distinctive cornoid lamellae comprising thin, columnar, closely stacked, parakeratotic cells extending through the stratum corneum with a minimal granular layer (Figure 2).
Clinical photograph. Dramatic regression of hyperkeratosis was noted at the 2-month follow-up visit, although mild local hyperpigmentation remained.
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A therapeutic trial of isotretinoin 1.5 mg/kg for 24 weeks (6 months) and 1.7 mg/kg for 8 weeks (2 months) resulted in dramatic regression of hyperkeratotic changes, although mild local hyperpigmentation remained at the 2-month follow-up (Figure 3).