An Unusual Presentation of Lichen Planus Pigmentosus Inversus Responsive to Topical Tacrolimus: A Case Report.

Background: Lichen planus pigmentosus inversus (LPPI) is a rare variant of lichen planus pigmentosus (LPP), characterized by sharply defined violaceous-brown to gray macules, papules, patches, or plaques primarily affecting the intertriginous and flexural areas. Unlike LPP, which predominantly affects Fitzpatrick skin types III to IV in sun-exposed areas, LPPI spares these regions and has been predominantly reported in White and Asian patients. Case Presentation: We discuss a 66-year-old man with Fitzpatrick skin type III who presented with a year-long history of mildly itchy, hyperpigmented plaques on the inframammary folds. These plaques developed after being hospitalized for a chronic urinary tract infection that was treated with antibiotics. He felt self-conscious and anxious due to the changes in skin, which affected his quality of life. His medical history included controlled diabetes and dyslipidemia, and he reported no systemic symptoms or prior topical medication use. A physical examination revealed well-demarcated, violaceous-brown plaques without scaling. Tests for fungal organisms, antinuclear antibodies, thyroid function, and hepatitis C were negative, and routine blood work was normal. A biopsy confirmed LPPI. Initial treatments with triamcinolone were ineffective, and hydroquinone was discontinued after 2 weeks due to irritation. The patient improved with tacrolimus 0.1% ointment twice daily, showing significant reduction in hyperpigmentation and improvement in skin texture at 4 and 8 weeks, with no side effects noted. Conclusion: This case report highlights the diagnostic and therapeutic challenges associated with LPPI and discusses its potential response to topical tacrolimus. Our findings indicate that tacrolimus 0.1% ointment provides a safe and effective nonsteroidal treatment alternative for LPPI. Given the possible impact of LPPI on quality of life, timely diagnosis and appropriate management are crucial. Due to the absence of established treatment protocols for LPPI, further studies are necessary to better understand treatment responses and guide therapeutic strategies, particularly for individuals with darker skin tones.