The epidemiology and etiology of facial onset sensory and motor neuronopathy (FOSMN), a rare syndrome that initiates with facial sensory disturbances followed by bulbar symptoms, remain unknown. To estimate the prevalence of FOSMN in Japan and establish the characteristics of this disease, we conducted a nationwide epidemiological survey. In the primary survey, we received answers from 604 facilities (49.8%), leading to an estimated number of 35.8 (95% confidential interval: 21.5-50.2) FOSMN cases in Japan. The secondary survey collected detailed clinical and laboratory data from 21 cases. Decreased or absent corneal and pharyngeal reflexes were present in over 85% of the cases. Electrophysiological analyses detected blink reflex test abnormalities in 94.1% of the examined cases. Immunotherapy was administered in 81% of cases and all patients received intravenous immunoglobulin. Among them, 35.3% were judged to have temporary beneficial effects evaluated by the physicians in charge. Immunotherapy tended to be effective in the early stage of disease. The spreading pattern of motor and sensory symptoms differed between cases and the characteristics of the motor-dominant and sensory-dominant cases were distinct. Cases with motor-dominant progression appeared to mimic amyotrophic lateral sclerosis. This is the first nationwide epidemiological survey of FOSMN in Japan. The clinical course of FOSMN is highly variable and motor-dominant cases developed a more severe condition than other types of cases. Because clinical interventions tend to be effective in the early phase of the disease, an early diagnosis is desirable.
Keywords: Amyotrophic lateral sclerosis; Blink reflex test; FOSMN; Nationwide survey.
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