Objective: To report a rare case of neuronal intranuclear inclusion disease (NIID) presenting with intractable resting and intention tremor.

Background: The NIID is a slowly progressive neurodegenerative disease characterized by localized neuronal loss and eosinophilic hyaline intranuclear inclusions in the central, peripheral nervous system cells, and also in visceral organs cells. The clinical manifestations of NIID are highly varied; disease onset occurs from infants to the elderly, and both familial and sporadic cases are reported (1).

Method: A 66-year-old man presented with slowly progressive resting, postural, and intention tremors in limbs and trunks, and unsteadiness since he was 46 years old. There were no other signs of Parkinsonism. His younger sister and brother had psychiatric disorder history. A neurologic examination disclosed mild cognitive function impairment, generalized hyper-reflexia, resting, postural, and intention tremors in limbs and trunks, and mild ataxic gait. He showed neither hypo-/brady-kinesia nor rigidity.

Results: Surface electromyography of the upper limb muscles showed discharges of muscle activity at frequencies of 3 Hz. Brain MRI demonstrated cerebral and cerebellar atrophy, and high-intensity areas in the medial part of the cerebellar hemisphere, the middle cerebellar peduncle, corpus callosum, and cerebral hemispheres on T2-weighted and fluid-attenuated inversion recovery images. Besides, MRI diffusion-weighted imaging (DWI) showed abnormal high-intensity signals along the cortico-medullary junction in the cerebrum. The 99mTc-TROADT-1 brain SPECT showed a mildly decreased uptake of radioactivity in both striatum. The spinocerebellar ataxia (SCA) gene panel, FMR1 premutation analysis, and LMNB1 gene duplication test all showed normal results. A diagnosis of NIID was finally made based on the skin biopsy histopathological findings.

Conclusion: This case implies that NIID can present with cerebellar form tremor that is similar to fragile X-associated tremor/ataxia syndrome (FXTAS). For clinical manifestations, neuroimaging finding, and neuropathology of FXTAS and NIID overlaps, genetic testing for FMR1 CGG repeat expansion is still mandatory for the differential diagnosis with FXTAS (2).

References: 1. Sone J, Mori K, Inagaki T, et al. Clinicopathological features of adult-onset neuronal intranuclear inclusion disease. Brain 2016;139:3170-86. 2. Padilha IG, Nunes RH, Scortegagna FA, et al. MR imaging features of adult-onset neuronal intranuclear inclusion disease may be indistinguishable from fragile x-associated tremor/ataxia syndrome. AJNR 2018;39:E100-1.

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MDS Abstracts - https://www.mdsabstracts.org/abstract/adult-onset-neuronal-intranuclear-inclusion-disease-presenting-with-intractable-resting-and-intention-tremor/