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.