[Refractory multiple myeloma with impaired consciousness accompanied by hyperammonemia and leukoencephalopathy-like findings].

A 81-year-old female was diagnosed with symptomatic multiple myeloma (MM; IgG κ type, D&S: IIB, ISS: 2) in August 2017. Although treatment with lenalidomide and dexamethasone was started, she developed deep venous thrombosis in the lower extremities as a complication; therefore, the treatment was changed to DBd. In February 2018, she required hospitalization due to general weakness and altered consciousness. Her IgG level and κ/λ ratio were elevated at 4,156 mg/dl and 605.56, respectively, revealing that MM was treatment-resistant. A protein-cell dissociation (cell blood count, 0/µl; protein, 100.6 mg/dl) was detected in the cerebrospinal fluid, whereas the ammonia level in serum was high (172 µg/dl). T2-weighted magnetic resonance imaging showed a broad range of high-density area in deep cerebral white matter suggesting leukoencephalopathy, whereas the cerebrospinal fluid was negative for JC virus. No pathological conditions causing secondary hyperammonemia were found. Although the involvement of drug-induced leukoencephalopathy in altered consciousness could not be ruled out since the chromosome with the normal karyotype at the first visit had a complex chromosomal abnormality, an originally minor clone of MM cells with a chromosomal abnormality might have contributed to the ammonia production resulting in altered consciousness.