Tacrolimus-associated Kaposi's Sarcoma in a Patient with Refractory Generalized Myasthenia Gravis: A Case Report

Kaposi’s sarcoma (KS) is an endothelial cell neoplasm that is rarely observed in patients with myasthenia gravis (MG). A 71-year-old Uyghur male diagnosed with myasthenia gravis type IVb was evaluated. In 2023, the patient experienced an exacerbation of muscle weakness and dyspnea secondary to an infection. Prior to this episode, he was treated with oral pyridostigmine bromide 90 mg four times daily and prednisone acetate 30 mg once daily. Subsequently, his regimen was adjusted to include tacrolimus capsules administered at 2 mg in the morning and 1 mg in the evening. In July 2023, he experienced another myasthenic crisis and received corticosteroid pulse therapy combined with a subcutaneous injection of Telitacicept, after which intermittent edema developed in both lower limbs. Since January 2024, the patient has experienced persistent, asymmetrical lower limb edema that has interfered with ambulation. Additionally, a localized non-blanchable red pigmented area was observed on the anterior tibia of the left lower limb. Serologic tests for HIV and syphilis were negative, and dermoscopic examination revealed multiple purple-red lacunae, irregular vascular structures, crust formation, and rainbow patterns on a blue-red background;—the biopsy reveal the basal layer of the epidermis shows increased pigmentation. In the dermis, there is a nodular infiltration of numerous spindle-shaped cells, with vascular-like clefts visible among them. Some of these clefts contain red blood cells, and a small amount of hemosiderin deposition is observed. Immunohistochemistry (IHC): CD34 positive, HHV-8 positive. In combination with the clinical presentation,findings suggestive of KS. Currently, with the discontinuation of tacrolimus, a slight improvement in skin pigmentation has been observed. In conclusion, KS is a rare complication arising during immunosuppressive therapy in patients with MG, and timely detection with regular screening is essential for optimizing patient outcomes.