Nationwide survey of patients with multisystem proteinopathy in Japan.

Objective: Multisystem proteinopathy (MSP) is an inherited disorder in which protein aggregates with TAR DNA‐binding protein of 43 kDa form in multiple organs. Mutations in VCP, HNRNPA2B1, HNRNPA1, SQSTM1, MATR3, and ANXA11 are causative for MSP. This study aimed to conduct a nationwide epidemiological survey based on the diagnostic criteria established by the Japan MSP study group. Methods: We conducted a nationwide epidemiological survey by administering primary and secondary questionnaires among 6235 specialists of the Japanese Society of Neurology. Results: In the primary survey, 47 patients with MSP were identified. In the secondary survey of 27 patients, inclusion body myopathy was the most common initial symptom (74.1%), followed by motor neuron disease (11.1%), frontotemporal dementia (FTD, 7.4%), and Paget's disease of bone (PDB, 7.4%), with no cases of parkinsonism. Inclusion body myopathy occurred most frequently during the entire course of the disease (81.5%), followed by motor neuron disease (25.9%), PDB (18.5%), FTD (14.8%), and parkinsonism (3.7%). Laboratory findings showed a high frequency of elevated serum creatine kinase levels and abnormalities on needle electromyography, muscle histology, brain magnetic resonance imaging, and perfusion single‐photon emission computed tomography. Interpretation: The low frequency of FTD and PDB may suggest that FTD and PDB may be widely underdiagnosed and undertreated in clinical practice. [ABSTRACT FROM AUTHOR]