Porokeratosis is a disorder of abnormal keratinization with multiple clinical variants. It is often difficult to achieve complete resolution of porokeratosis even with a variety of therapies that have been reported to have some efficacy. Report of a CaseA woman in her 40s with no significant medical history was referred for evaluation of a painful dermatitis on her left arm. Approximately 1 year earlier, a painful, pruritic, erythematous papule had developed on her left arm, which subsequently spread into a linear array of papules extending from her left wrist up her arm to her neck, associated with pruritus, paresthesias, and pain; 3-to 10-mm erythematous papules with overlying scales were arranged in a linear pattern extending up the ventral part of her arm, across her shoulder to the left side of her neck and chest ( Figure 1). Several lesions exhibited an outer hyperkeratotic rim. She had similarly shaped areas of hyperpigmentation without overlying epidermal change on her left arm and on the left side of her chest and neck.A skin biopsy sample revealed a vertical column of parakeratosis within the stratum corneum, an absent granular layer underlying the column, and a focal lymphohistiocytic infiltrate underlying the epidermal change. The clinical and histopathologic features confirmed a diagnosis of linear porokeratosis. The patient had been treated with betamethasone dipropionate, 0.05%, ointment for several months with minimal improvement; oral acitretin treatment was subsequently started at 25 mg/d. After 3 months of acitretin treatment, she had no improvement of the lesions on her arm but had adverse effects, including scaling of her palms and soles and dryness of her lips and face.We continued daily treatment with betamethasone dipropionate, 0.05%, ointment and added tacrolimus, 0.1%, ointment, administered twice daily, to the patient's treatment regimen. Oral acitretin treatment was discontinued because it had caused adverse effects with no skin improvement. With the combination of betamethasone and tacrolimus, the skin lesions improved rapidly and dramatically. At the 2-month follow-up examination, the patient had hyperpigmented macules and patches in a linear pattern up the ventral side of her left arm and across the shoulder to her neck on the left side, consistent with postinflammatory hyperpigmentation. The inflammation had completely cleared. In addition to improved skin lesions, the patient reported complete resolution of associated pain, pruritus, and paresthesia.The patient was followed up at 3-to 6-month intervals for 2½ years, during which her skin showed continued improvement. Tacrolimus treatment was tapered down to once-daily administration to areas of postinflammatory hyperpigmentation and any new lesions, with betamethasone used only on new lesions. At 2½-year follow-up, the daily tacrolimus treatment was discontinued. At examination, the patient's skin was essentially back to baseline, with only a few very faint reticulated pale-brown macules (Figure 2), thus demonstrating the long-ter...