Plasma Cell Balanitis Unresponsive to Topical Corticosteroids: Combined Efficacy of Tacrolimus and Emerging Evidence for Underrecognized Intrinsic Resistance to Corticosteroids.

Plasma cell balanitis (PCB), also known as Zoon's balanitis, is a chronic, benign inflammatory dermatosis affecting the glans penis, mainly occurring in uncircumcised middle-aged men. Currently, there has been no recommended and standardized treatment. Topical corticosteroids are the most common first-line therapy in clinical practice but often account for the primary inefficacy relapse and adverse events, particularly in cases requiring long-term use due to the high transcutaneous absorption in the penile skin. A series of recent case reports may suggest topical calcineurin inhibitors as a promising alternative, offering significant improvement in corticosteroid-resistant cases. In this paper, we describe a 61-year-old uncircumcised male patient with a one-year history of asymptomatic erosive erythema on the penis, which was initially unresponsive to topical corticosteroids. Lesional skin biopsy histologically confirmed a diagnosis of plasma cell balanitis. Combined treatment of a preceding topical corticosteroid with 0.1% tacrolimus ointment led to a dramatic clinical response within two weeks of treatment, followed by almost complete resolution after six weeks. This approach enabled the maintenance of the treatment efficacy with a weak-potency corticosteroid throughout the clinical course. Recurrence occurred with reduced application frequency, but the daily use of the same regimen rapidly restored favorable disease control. We discuss the potential difficulty in managing PCB, with particular interest in the relatively high frequency of corticosteroid resistance in nearly half of the cases reported to date. This paper also updates the possible mechanisms of action and clinical benefits of topical calcineurin inhibitors in plasma cell biology.