ABSTRACT
Clinical diagnosis PSP is frequently misdiagnosed, most commonly as PD, but when PSP is considered, its distinctive features usually make it possible to make a confident diagnosis (see Box 13.1). Most patients present with gait disturbance and unsteadiness with a tendency to fall backwards. The gait has a characteristic reeling or staggering quality, due to the stifi posture of the trunk and neck with irregular large steps forwards, which allow a distinction to be made from the veering broad-based gait of cerebellar ataxia. Some patients present with early complaints of visual disturbance which are related to fixation instability and disruption of the control of saccadic eye movements. Unfortunately, as visual acuity itself is not affected by PSP, these symptoms may be initially thought to be psychogenic in origin until the typical disturbance of downward gaze emerges. The neuro-ophthalmological features of patients with established PSP are usually clear-cut.11 Frontalis overactivity and a diminution of the blink rate to less than 4/minute lead to a 'surprised' facial appearance. Eye opening may be impaired either by active involuntary contraction of orbicularis oculi (blepharospasm) or by inability to voluntarily open the eyes (,apraxia of eyelid opening') (see Figure 13.1).12 Fixation on a stationary object may be interrupted by visible constant velocity saccadic intrusions in which the gaze is diverted briefly away and then back to the target, described as square wave jerks.13 In the earliest stages of the disease there may be slowness of vertical saccadic eye movements which progress to limitation of downwards vertical saccadic eye movements and then to a complete vertical gaze palsy.11 The doll's head manoeuvre may be used to generate a normal vertical vestibular-ocular response demonstrating the integrity of the third nerve nuclei and confirming that the eye movement disorder is supranuclear. Some limitation of upgaze is a frequent accompaniment of normal ageing and may be seen in PD; limitation of downgaze is a much more specific finding suggestive of PSP. In the late stages of the disease, involvement of the horizontal eye movement system may lead to a complete supranuclear gaze palsy.11
