**5. Clinical features**

#### **5.1. Gait disturbance**

Gait disturbance is usually the commonest and earliest symptom of INPH. Its onset is insidious over months and sometimes years. It is also the one that is most likely to respond to shunting. The gait impairment in NPH is frequently described as 'apraxic'. Other descriptors used are 'shuffling', 'magnetic' and 'broad‐based'. Thompson [29] is in favour of the term 'frontal lobe ataxia' instead of gait apraxia, which is defined as an impairment of gait not attributed to motor or sensory deficits, although he acknowledges that this is based on observation rather than on firm evidence for this. Interestingly, some patients display normal ability to move the legs in a recumbent position while being practically unable to walk. This phenomenon indicates that the gait disturbance is due to a problem with locomotion rather than a pure motor dysfunction. There is no single feature that is pathognomonic of the gait disturbance in NPH. In mild cases, patients may display a broad‐based gait but in more severe cases there is a reduction in stride length [30]. The feet appear clumsy and there is difficulty initiating foot movements. Patients are also slow to rise from a seated position. The gait is also characterised by reduced step height and a typical disturbance of the dynamic equilibrium [31]. About 30% of patients experience freezing of gait [31]. Patients tend to turn in multiple small steps. Postural instability and falls are common. The gait pattern in INPH is visibly different from that of Parkinson's disease [31]. A wider step, as well as increased foot angles, is uncharacteristic of Parkinson's disease but common in INPH. Upper limb movements are preserved. The reason is that the motor fibres controlling the upper extremities and face originate more laterally in the motor cortex and are subsequently subjected to less stretching due to hydrocephalus [32]. Upper motor neuron signs, such as spasticity and hyperreflexia, are unusual. Since the symptoms of INPH are symmetrical, any lateralising signs should raise suspicion of other disorders.

### **5.2. Dementia**

are already maximally dilated, and this would explain the loss of autoregulation [23]. When the arterioles are obstructed, venous collapse ensues, followed by impaired CSF drainage and ventricular enlargement [23]. The problem we have with this hypothesis is that if one wants a unifying theory with ischaemia as the initiating trigger, one would struggle to explain the appearance of NPH in disorders such as progressive supranuclear palsy (PSP), corticobasal degeneration (CBD) and Alzheimer's disease (AD). Periventricular white matter ischaemia is an uncommon finding especially in PSP and CBD. Yet, there has to be a final common pathway which results in hydrocephalus in all these conditions. We hypothesise that neurodegeneration has a role to play in INPH, at least in some cases. The following findings would support this: **•** Of the 38 patients in two studies who were diagnosed with INPH, vascular changes (71%), AD (61%), PSP (2.6%) and CBD (2.6%) were the most frequent co‐existing pathologies and

none had specific neuropathological changes to suggest INPH as an entity [24, 25].

**•** Midbrain atrophy is strongly associated with gait disturbance in NPH [28].

in INPH than in those with established AD [27].

underlying these symptoms.

532 Update on Dementia

deteriorate less rapidly (e.g. AD).

**5. Clinical features**

**5.1. Gait disturbance**

VD‐associated NPH, AD‐associated NPH, etc.

**•** Levels of tau protein in CSF, an index of neuronal degeneration, were found to be higher in patients with NPH compared to healthy controls [26] although phospho‐tau181 was lower

**•** Although the gait disturbance improves with shunting, the dementia seen in INPH often does not and it continues to progress, suggesting a difference in the aetiopathogenesis

**•** Even if there is an initial response, overall the condition eventually progresses despite a functioning shunt in situ in the majority of cases. It is therefore possible that those who deteriorate quicker also have more rapid neurodegeneration (e.g. PSP) than those who

Finally, we take the opportunity to emphasise the possibility that INPH has different causes which form a pathophysiological continuum. This would not only explain the differences with shunt response and rates of progression but would also explain why a universal theory remains elusive. It would perhaps be more appropriate to refer to these conditions, where known, as

Gait disturbance is usually the commonest and earliest symptom of INPH. Its onset is insidious over months and sometimes years. It is also the one that is most likely to respond to shunting. The gait impairment in NPH is frequently described as 'apraxic'. Other descriptors used are 'shuffling', 'magnetic' and 'broad‐based'. Thompson [29] is in favour of the term 'frontal lobe ataxia' instead of gait apraxia, which is defined as an impairment of gait not attributed to motor or sensory deficits, although he acknowledges that this is based on observation rather than on firm evidence for this. Interestingly, some patients display normal ability to move the legs in

The cognitive deficits in INPH are classically that of a subcortical dementia with predomi‐ nantly frontal features [33–35] and are characterised by apathy, inattention, psychomotor retardation and poor executive function [36]. It is worth noting that the term 'dementia' is used to designate the cognitive impairment in INPH although some patients who present early may not have evidence of this or may not meet the criteria for dementia on cognitive testing. Saito et al. have shown that the deficits extend beyond executive function, attention and memory to visuoperceptual and visuospatial domains on neuropsychological testing [37]. There is substantial overlap between INPH and AD but frontal lobe dysfunction account for >50% of the cognitive deficit in INPH while memory impairment is responsible for >50% of the cognitive deficit in AD [37]. The degree of neuropsychological impairment in INPH has also been found to relate to the severity of other signs of INPH [38]. Those with vascular risk factors performed worse than those without [38]. Compared with Binswanger's disease, impairment of memory and visuospatial attention in NPH may be more pronounced [39].

#### **5.3. Urinary incontinence**

Urinary incontinence is often the last symptom to appear, although it is well established that each symptom can occur independently of the others [40]. Increased urinary urgency occurs earlier and is almost always present in INPH [40, 41]. Urinary incontinence is also very common in the elderly and therefore, on its own, lacks specificity. Fisher [40] considered it to be a frontal lobe incontinence as patients were indifferent regarding where and when to urinate. This correlates with the pattern of cognitive deficits mentioned earlier. Sakakibara et al. [42] have found that detrusor overactivity, seen in 95% of their cases, is fundamental to the appearance of urinary urgency, frequency and incontinence. Seventy‐one per cent had voiding symptoms such as difficulties in initiating urination and poor flow [42]. Bladder dysfunction can improve after shunting suggesting that the symptoms are likely secondary to impaired cerebral control of bladder storage. The underlying mechanism for detrusor overactivity in patients with NPH appears to be related to reduced cerebral blood flow in the right frontal cortex, and to a lesser extent impaired basal ganglia function [43]. Reduced mobility could also be contributing to incontinence in these patients [43].
