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A 69-year-old man with a 10-year history of localisation-related epilepsy with secondary generalisation, and a 1-year history of right occipital haemorrhage presented with cognitive impairment, insomnia, visual hallucinosis and shortened stride. Examination suggested encephalopathy with subtle appendicular myoclonus and left hand postural and classical rest tremor, asymmetrical bradykinesia, neck and limb rigidity and left-sided neglect. Saccadic eye movements were entirely normal for approximately 5 years of follow-up. Sagittal T1 imaging (see figure 1A) demonstrated midbrain atrophy suggestive of the ‘hummingbird’ sign of Progressive Supranuclear Palsy (PSP) in the context of diffuse hemispheric foci of susceptibility artefact (see figure 1B) secondary to microhaemorrhages from cerebral amyloid angiopathy (CAA). 123I-Ioflupane single-photon emission computed tomography (SPECT) (DaTSCAN) was performed and demonstrated significant reduction in radiotracer uptake in the striatum bilaterally. Significant reduction in radiotracer uptake in the posterior striatum, particularly on the right was noted. The DaTSCAN was graded as upper range of grade 2 out of 3 by qualitative assessment according to the Catafau classification.1
This case of CAA with Parkinsonism is noteworthy in that the Parkinsonian phenomenology described is more suggestive of an idiopathic or symptomatic aetiology rather than PSP, and challenges the apparent 100% specificity of the ‘hummingbird sign’ for PSP as demonstrated recently in a clinical, radiological and pathological study of 41 cases of atypical Parkinsonism.2
The degree of midbrain atrophy seen in this case may reflect chronic Wallerian degeneration secondary to extensive cortical involvement in CAA, and cortical involvement is the likely cause of the appendicular myoclonus seen on clinical examination. The hummingbird appearance in PSP relates to atrophy of the midbrain tegmentum.3 Additionally, there is a relative lengthening of the interpeduncular fossa compared with the anteroposterior diameter of the midbrain tegmentum itself.3 To further demonstrate the diagnostic utility of MRI brain imaging in PSP, and supplementing the hummingbird sign which is essentially a qualitative finding, studies have looked at regional MRI measurements of brainstem structures in order to identify quantitative indicators of PSP.3 Various brainstem measurements have been studied in subjects with PSP, versus idiopathic Parkinson's disease (IPD) and controls. Kato et al3 performed a morphometric analysis of midsagittal MRI images in patients with PSP and noted that all had the hummingbird sign. Additionally, there was a significant reduction in the areas (mm2) of the midbrain tegmentum, inferior colliculus and pontine tegmentum compared with IPD and controls.3 Such areas may not be practically quantified on routine conventional MRI, however, the authors did note that the mean length (mm) of the anteroposterior diameter of the midbrain tegmentum in PSP patients was significantly shorter than in IPD patients and controls.3
The anteroposterior diameter of the midbrain is a measurement that could be relatively easily performed on routine diagnostic imaging, and Warmuth–Metz et al have studied this in addition to the anteroposterior diameter of the pons and collicular plate in 50 individuals with a variety of Parkinsonian syndromes including PSP, IPD and the striatonigral variant of multiple-system atrophy (MSA-P).4 They identified that patients with PSP had significantly lower midbrain diameters (mean 13.4 mm, range 11–15 mm, p<0.001) compared with patients with IPD (mean 18.5 mm, range 17–19 mm) and controls (mean 18.2 mm, range 17–20 mm).4 The anteroposterior diameter of the pons was defined as the largest distance perpendicular to the floor of the fourth ventricle, and this was significantly smaller in patients with PSP and MSA-P compared with those with IPD or control subjects (p<0.001).4 There was, however, significant overlap in individual values between all four groups of patients such that the authors concluded that measuring pontine diameter did not add significant information to the measurement of midbrain diameter alone in patients with PSP.4 In the case we describe, the anteroposterior diameter of the midbrain measured 14.7 mm within the range described in PSP cases, and anteroposterior diameter of the pons was 25 mm within the control range identified by Warmuth–Metz et al.4 This case highlights the importance of correlating imaging findings with clinical phenomenology, as in the case of dual pathology, such as CAA and IPD, classical imaging findings may be absent or their significance altered.
Contributors JJM drafted the original manuscript, and it was reviewed and critiqued by AM, EK and TL.
Funding JJM, AM and EK report no disclosures. TL receives honoraria from Abbot, Boehringer Ingelheim, Lundbeck and Orion. He has received educational grants from Bayler Schering, Biogen Idec, Lundbeck and Medtronic. He has received grants from the Irish Institute of Clinical Neuroscience, the Mater College and PRTL1 funding. TL sits on the advisory boards of Abbot, Novartis, UCB Pharma, Teva, Merck Serono and Biogen Idec.
Competing interests None.
Patient consent Obtained.
Provenance and peer review Not commissioned; externally peer reviewed.
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