Objective: To describe a patient with late onset, sporadic NIID who had a tremor as his first complaint.

Background: NIID is a rare, slowly progressive neurodegenerative disorder characterized by the presence of eosinophilic intranuclear inclusions. Diagnosis is via skin biopsy and is suggested for by characteristic MRI brain appearances. The clinical phenotype of adult-onset sporadic onset NIID has only been recently defined with dementia as a prominent feature.1  Urinary incontinence, peripheral neuropathy and other movement disorders  are frequently observed.  To date, a postural and kinetic tremor akin to “ET” has not been described.

Methods: Case report

Results: A 70 year old male first presented at age 61 with a new onset tremor. There was no family history and the tremor did not improve with alcohol. A mild bilateral postural and kinetic tremor was observed. No Parkinsonian features were detected. The tremor remained stable for 8 years until he represented again at the age of 69 with a year’s history of worsening tremor associated with short term memory loss. A moderate postural and kinetic tremor was now seen with worsening spiral scores. Detailed neuropsychological testing revealed significant impairment in tests of visual and verbal memory. MRI brain imaging showed leukoencephalopathy and DWI hyperintensity in the subcortical U fibres suggestive of the diagnosis of NIID which was confirmed by a skin biopsy. Further evaluation revealed the presence of previously undetected neurogenic bladder requiring intermittent catheterization.

Conclusions: Here, we present a unique case of NIID first presenting with an ET phenotype. The ET phenotype has not been previously described in NIID.

The concept of a late onset ‘aging related tremor’ (ART) has been recently proposed: severity of tremor based on spiral drawing was shown in a large cohort study to be correlated with worsening aging parameters including cognitive decline and increased mortality that was not observed in classical ET.2 It remains controversial whether ART is distinct from ET or that this entity is a late-onset variant of ET. 

Our case provides support to the hypothesis that ART is not a benign entity, particularly as the tremor worsened in parallel with the onset of overt cognitive decline. The diagnosis of late onset ET should be made with caution and other conditions should be excluded.

References: 1.            Sone, J. et al. Clinicopathological features of adult-onset neuronal intranuclear inclusion disease. Brain (2016).

2.            Deuschl, G , Petersen, I, Lorenz, D, et al. Tremor in the elderly: Essential and Aging-Related Tremor. Movement Disorders (2015).   

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MDS Abstracts - https://www.mdsabstracts.org/abstract/essential-tremor-as-a-presenting-symptom-of-neuronal-intranuclear-inclusion-disease-niid/