We herein report a case of Human T-lymphotropic virus type-I (HTLV-I)-associated myelopathy with bulbar palsy-type amyotrophic lateral sclerosis-like symptoms. A 52-year-old woman developed dyslalia at approximately 40 years of age, which slowly progressed. She presented with muscular atrophy and increased tendon reflexes of the extremities as well as bulbar palsy, from which motor neuron disease was suspected. Cerebrospinal fluid (CSF) testing revealed no abnormalities except for an elevated neopterin concentration at 143.17 pmol/mL (normal ≤30 pmol/mL). Her serum and CSF anti-HTLV-I antibody titers were also high. Intravenous infusions of methylprednisolone decreased the CSF neopterin concentration to 50.33 pmol/mL. Subsequent oral prednisolone therapy was effective in alleviating the symptoms.