Unusual case of idiopathic normal pressure hydrocephalus initially presenting as Parinaud’s syndrome?

Abstract

Dear Editor, I read with great interest the article by Lee et al. in which they report an extremely interesting case of normal pressure hydrocephalus (NPH) with a clinical presentation of Parinaud’s syndrome (PS). However, I would like to make some comments hoping to provide a better understanding of the case and related issues. First, I believe that there might be some questions regarding the evaluation and diagnosis of the patient. The authors describe the clinical presentation of the patient as PS and associate it with NPH. In my opinion, there might be some questions about evaluating this phenomenology as Parinaud’s syndrome, considering that the other basic components of PS including convergenceretraction nystagmus and light-near dissociation were lacking in this patient. However, as also referenced by the Authors, in a recent crucial review, it was found that the classical triad of PS was present in just 65% of cases. Nevertheless, PS can also be defined as supranuclear vertical gaze palsy, and dorsal midbrain lesion is a constant etiology of PS, as also found in the 40 consecutive adult patients in the same report by Shields et al. Therefore, I believe that defining the clinical presentation of this patient as PS, based solely on upward gaze palsy and without supporting neuroimaging data, might not be rationale. The clinical presentation of the patient included gait impairment, postural instability and supranuclear palsy, which are also common features of progressive supranuclear palsy (PSP). In addition, slurred speech and bilateral rigidity–bradykinesia were also mentioned, which are also often encountered in patients with PSP (and atypical for NPH). Therefore, I believe that the presence of an underlying neurodegenerative disease, such as PSP, is a highly possibility that is rather underestimated in the report. The authors state that brain magnetic resonance imaging showed no structural lesions on the dorsal midbrain. In contrast, I believe that the sagittal T1-weighted image illustrated in the article did show a significant midbrain atrophy that might resemble the hummingbird sign in PSP. The authors remark on the improvement of the upward gaze palsy and gait difficulty after the ventriculoperitoneal shunt as points supporting the diagnosis of idiopathic NPH. However, as far as can be seen from Figure 1a and Figure S1, I do not agree that there is a considerable improvement in conjugate upward gaze palsy after ventriculoperitoneal shunt surgery. Furthermore, considering that this is a unique and extremely interesting presentation, I would like to remark that video recordings of the preoperative gait disturbance and postoperative improvement were not shown in the report, which surely constitutes a major limitation of this report. In contrast, I believe that the co-occurrence of PSP and NPH cannot be excluded in that patient, which is an new and interesting argument (co-occurrence of NPH and other neurodegenerative disorders) discussed in recent reports. Remarkably, in a critical review by Espay et al., it was emphasized that truly idiopathic NPH represents a diagnosis of exclusion that requires careful consideration of neurodegenerative disorders, most often Alzheimer’s disease, dementia with Lewy bodies and PSP. They have pointed out their long-term institutional experience regarding the follow up of post-shunt patients, in which they found that the initial diagnosis of idiopathic NPH persist in just 32% of patients at 36 months interval after shunt operation and a revised diagnosis (Alzheimer’s disease, dementia with Lewy bodies, PSP) was received in >25% of patients. In conclusion, they postulated a new view that certain neurodegenerative phenotypes might present with ventriculomegaly, a veritable neurodegenerative NPH (distinct from the idea of NPH cases with ‘dual’ pathology). Based on these interesting discussions, I wonder if the authors might include the detailed preoperative and postoperative video recordings of neurological examinations of the patient that would surely provide a much better understanding of the case. Of note, the long-term follow up of the patient might also give substantial data in this regard. Finally, they illustrated their effort for distinguishing the disease from dopa disturbances by reporting the results of normal striatal dopamine transporter. The Authors stated that striatal dopamine depletion was not found in the patient, and remarked on this as evidence to consider the diagnosis of PSP as highly unlikely. However, although the results of recent studies have remarked on reduced striatal DAT binding as supportive data for a diagnosis of PSP-Richardson’s syndrome, the utility of this finding in the diagnosis of the other variant syndromes of PSP ; PSP-PGF as PSP with progressive gait freezing ; PSP-P as PSP-parkinsonism is controversial. Remarkably, in another crucial report, striatal dopamine transporter activity was found to be a non-specific method for differentiating among atypical parkinsonian syndrome subgroups.