Materials and methods

PATIENTS

Since 1993 brains from necropsies have been sent to the German reference centre for spongiform encephalopathies for the diagnosis of Creutzfeldt-Jakob disease or genetic prion disease. Most patients necropsied were examined as suspected CJD cases during their lifetime by a study physician of the German CJD surveillance unit.

We collected clinical data from patients in whom CJD was ruled out by neuropathology, and in whom AD or DLB were confirmed.

The control group of 25 patients with definite sporadic CJD was recruited from patients consecutively referred to the CJD surveillance unit in the same period as the patients with AD and those with DLB. Recruitment of patients with CJD ceased as soon as a representative group of patients was achieved that corresponded in clinical signs and symptoms to our previous findings.1 Patients with genetic14 or iatrogenic prion disease were excluded.

ANALYSIS OF CLINICAL DATA

Medical records of all patients were studied retrospectively. Each patient's chart was analysed with a standardised checklist, which contained the following items:

(1) Reason for sending in material for prion disease analysis.

(2) Signs and symptoms typical for CJD were rated according to modified Masters criteria.1 15-17 Extrapyramidal signs were subdivided into limb rigidity, parkinsonism, and dystonic, choreatic, athetoid or ballistic movements. Visual disturbances included deteriorated or blurred vision, visual field restriction, and disturbed perception of structures and colours. Visual hallucinations were rated separately.

Clinical features of AD were rated according to NINCDS-ADRDA criteria.4

Clinical features of DLB were noted according to McKeithet al.5 18

(3) Technical investigations: All EEGs were initially reviewed by one of us (SP). The EEGs were additionally reviewed without knowledge of clinical information by a second observer (BJS).19 20“CJD typical EEG” was diagnosed in EEG tracings fulfilling Steinhoff's criteria. Testing for protein 14–3–3 and neuron specific enolase (NSE) in CSF was performed as previously described.16 A cut off for CJD was defined as NSE concentration>35 ng/ml in CSF.16

CLINICAL CLASSIFICATION OF PATIENTS

Using the results from the above checklist, patients were classified according to international diagnostic criteria for CJD,15 16 AD,4 and DLB.5 Each patient was clinically classified for all three dementia entities. The categories “possible”, “probable”, and “other disease” (not fulfilling the criteria) were used to express the degree of certainty in the clinical diagnosis.

NEUROPATHOLOGICAL EVALUATION

Brains were fixed in 10% formalin for at least 14 days. Representative blocks were cut, decontaminated for 1 hour in concentrated formic acid,21 and embedded in paraffin. Whenever possible recommended regions according to the consensus criteria for diagnosing AD and DLB were used.5 22Paraffin sections (2 μm) were stained with haematoxylin and eosin and with Bielschowsky methods.

Immunocytochemistry was performed with monoclonal antibodies against a synthetic peptide corresponding to 138–152 of the human prion protein (Gö138, Göttingen, Germany), β-amyloid (βA4, Boehringer Mannheim, Germany), phosphorylated tau (AT8, Innogenetics, Ghent, Belgium), and a polyclonal antiserum against α-synuclein (Q698, MPI Göttingen, Germany).

NEUROPATHOLOGICAL DIAGNOSTIC CRITERIA

Prion diseases

The definite diagnosis of prion disease is based on the detection of prion protein (PrP) deposits using PrP immunocytochemistry.23

Alzheimer's disease

Alzheimer's disease related pathology was classified using the CERAD pathological criteria based on semiquantitative analysis of neuritic plaques (Bielschowsky stain, αA4 immunostain)24as well as the Braak and Braak classification based on the distribution of neurofibrillary tangles and neuropil threads (Bielschowsky stain, AT8 immunostain).25

The 19 cases of AD were subclassified as CERAD C/Braak and Braak stage V-VI (n=14) and CERAD B/Braak and Braak stage III-IV (n=5).

Dementia with Lewy bodies

Distribution and frequency of Lewy bodies (LBs) were evaluated according to the consensus criteria for diagnosing DLB.5The number of LBs were counted in the brain regions determined in the protocol (α-synuclein immunostain) and converted into scores from 0 (no LBs), 1 (1–4 LBs), and 2 (>5 LBs) for each area. Based on the total score, cases were divided into three subtypes: brainstem dominant, limbic, and neocortical.

The 12 cases of DLB examined here were subclassified as neocortical (n=10) and limbic (n=2) subtypes.

GENETIC ANALYSIS

A screening of mutations in the prion protein gene (PRNP) was performed in 20 patients with CJD using single strand conformation polymorphism (SSCP) analysis or direct DNA sequence analysis, as described previously.14 No mutations in PRNP were detected in the patients included in this study.

Results

PATIENTS

From June 1993 to June 1997 brain tissue from 413 suspected cases of CJD was examined in the German reference centre for spongiform encephalopathies. In 309 cases, sporadic CJD or genetic prion disease was confirmed; in 104 cases prion disease was ruled out. In these 104 cases, Alzheimer's disease was most often diagnosed (28 cases), followed by dementia with Lewy bodies (14 cases).

Nine patients with AD and two patients with DLB were excluded from the analysis because details of clinical examination were absent. Nineteen patients with AD and 12 patients with DLB were included in this study. Among these necropsy confirmed patients, 14 with AD and five with DLB were seen prospectively by a member of the epidemiological CJD surveillance unit. The medical records were obtained from the remaining patients.

Twenty five patients with confirmed CJD served as a control group.

CLINICAL CHARACTERISTICS

In the CJD group, women and men were affected similarly (female:male=13:12), whereas women were overrepresented in the AD group (15:4) and less often diagnosed with DLB (4:8). The patients with CJD were younger (median 64 years, range 23–76 years) than the patients with AD (76 years, 25–85 years) and patients with DLB (72 years, 60–81years).

The median duration of illness varied from 4 months (range 2–24 months) in patients with CJD to 18.5 months (range 1–60 months) in patients with DLB and 24 months (range 3–108 months) in patients with AD. A patient with AD was suspected of having CJD after 9 years of disease course when he developed rigidity and myoclonus.

REASONS FOR SUBMITTING BRAIN TISSUE FOR PRION DISEASE ANALYSIS

Patients with CJD (n=25)

In 20 patients the primary clinical diagnosis was CJD, the remaining five patients were referred as patients with suspected CJD with other differential diagnoses.

Patients with AD (n=19)

Nine patients had rapidly progressive dementia with or without focal neurological signs and the EEG showed sharp wave complexes; therefore CJD was clinically suspected. “Probable” CJD was diagnosed in five of these patients with AD as sharp wave complexes fulfilled criteria for periodicity.19 In 10 further patients CJD was considered in the differential diagnosis as the disease course was very rapid.

Patients with DLB (n=12)

One patient's clinical diagnosis by the notifying hospital was CJD, because of rapidly progressing illness with dementia, parkinsonian syndromes, and myoclonus, but without specific EEG findings. In the remaining patients CJD was suspected because of rapid progression of disease, and/or the development of myoclonus. In two of these patients, EEG showed sharp wave complexes, one of those fulfilled criteria for periodicity; therefore in this patient CJD was clinically “probable”.

CLINICAL SIGNS AND SYMPTOMS AT ONSET OF DISEASE

The details are listed in table 1. Dementia was the first sign of disease in most patients with AD and those with DLB and in 44% of patients with CJD. Whereas patients with AD or with DLB often had dementia only, in many patients with CJD, dementia was accompanied by neurological signs or symptoms, or neurological signs preceded dementia.

CLINICAL SIGNS AND SYMPTOMS DURING THE COURSE OF DISEASE

All patients developed dementia. Myoclonus and extrapyramidal signs were especially common in patients with CJD and patients with DLB (>80% and >70% respectively) and in more than 50% of patients with AD (see table 2 for details). Extrapyramidal signs in patients with AD and with DLB were restricted to limb rigidity (>50% respectively) and parkinsonism (58% in patients with DLB, 8% in CJD, and 11% in AD). Patients with CJD additionally showed hyperkinetic signs (40%). Nearly all patients with CJD and 37% of patients with AD had cerebellar signs, not noted in DLB. Visual disturbances such as loss or deterioration of vision, visual field restriction, or disturbed perception of colours and structures were exclusively found in CJD (44% of patients).

Signs typical of DLB such as fluctuations of cognitive impairment were found in 58% of patients with DLB, but only in one patient with AD and no patients with CJD. Visual hallucinations were most common in DLB (58%), but were also present in CJD (36%) and AD (11%). Referring physicians did not report neuroleptic hypersensitivity in any patient, including nine patients with DLB (75%), six patients with AD (32%), and one patient with CJD (4%) who had received neuroleptic medication.

RESULTS OF TECHNICAL INVESTIGATIONS

Periodic sharp wave complexes19 were present in 56% of patients with CJD, 31% of patients with AD, and 8% of patients with DLB (fig 1 A and B, table 3).

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Figure 1

CJD typical periodic sharp wave complexes in EEGs from (A) a histologically proved AD patient, aged 76 years after 4 months of disease (EEG curves by courtesy of Dr E Banzhaf). (B) A histologically proved patient with DLB, aged 77 years, after 36 months of disease (EEG curves by courtesy of Professor R Benecke).  

Protein 14–3–316 was detectable in CSF in 87% of patients with CJD, 20% of patients with AD and in none of the five patients with DLB tested. The median of NSE16 was pathologically high in patients with CJD, but normal in patients with AD and those with DLB. According to previously established tests in our laboratory using an NSE value in CSF greater than 35 ng/ml as a cut off indicative for CJD, 73% of patients with CJD (16/22) had pathological NSE values, but only one of six patients with AD and none of the five patients with DLB tested did so. One patient with AD had CSF taken 4 days after an epileptic seizure. In this patient the protein 14–3–3 was detectable and NSE of 120 ng/ml was pathologically high. False positive results in CSF testing are known after epileptic seizures.16 The other patient with AD with detectable protein 14–3–3 in CSF had a normal NSE value.

CLINICAL CLASSIFICATION OF PATIENTS

Patients with definite CJD

”Probable” CJD was diagnosed in 84% of patients with CJD. In 16% (4/25) of patients with CJD technical investigations were not typical for CJD; therefore CJD was “possible”. According to the diagnostic criteria for AD the diagnosis of AD was “probable” in 24% of cases. Sixteen per cent of patients with CJD fulfilled clinical criteria for “possible” DLB (dementia and visual hallucinations or parkinsonism).

Patients with definite AD

In 16% of patients with AD the diagnosis of “possible” CJD was made, in 26% “probable” CJD was diagnosed clinically; 74% of patients with AD fulfilled clinical criteria of “probable” AD; one patient with AD (5%) met the criteria for “probable” DLB (dementia, fluctuations, parkinsonism, and visual hallucinations); and one patient met the criteria for “possible” DLB (dementia and visual hallucinations). In another patient with AD, dementia had preceded the development of parkinsonism by 9 years, so that in this case parkinsonism was not rated for the diagnosis of DLB.5

Patients with definite DLB

”Possible” CJD was diagnosed in 50% of patients with DLB, but only one patient with DLB had CJD typical PSWCs in EEG recordings and was therefore clinically “probable” CJD; 58% of patients with DLB met criteria for “probable” AD; 84% of patients with DLB fulfilled clinical criteria for “possible” or “probable” DLB (42% each, fig 2).

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Figure 2

Clinical classification of necropsy proved patients. All patients were clinically classified as to whether CJD, AD, or DLB were clinically possible, probable, or not present.

Discussion

Our series is the first to describe clinical findings on a large number of patients erroneously suspected of having Creutzfeldt-Jakob disease, who were histologically proved to have Alzheimer's disease or dementia with Lewy bodies. We are aware of only three comparable series26-28 that report necropsy results of suspect patients with CJD who had other final diagnoses. Detailed clinical information was not given in these series. In all studies, AD was the most frequent alternative diagnosis; DLB was not mentioned, as it was only recently defined as a separate diagnostic entity.

As shown in clinicopathological studies,7 28 29 clinical diagnosis in patients with dementia has become increasingly accurate, ranging from a specificity of 95% in CJD28 and 90%-97% in DLB7 to 79%29 in AD. Thus, patients with typical clinical presentation seem to be sufficiently covered by current diagnostic criteria. However, differential diagnosis is a major challenge in atypical cases, such as patients with rapidly progressive AD or DLB or patients with slowly progressive CJD.

In our study, CJD was suspected in patients with AD or DLB if the disease course was rapid or patients developed focal neurological signs, especially myoclonus, or if EEG was considered to point to CJD.

In most patients with AD or with DLB, dementia was present already at the onset of disease, corresponding to the literature.4 13 By contrast, patients with CJD additionally had focal neurological signs such as gait or visual disturbances. During the course of disease dementia, myoclonus, and limb rigidity were the overlapping features of the three patient groups. Due to selection of “CJD-like” cases myoclonus was more common in DLB (75%) and AD (58%) than usually reported (19% in DLB19 and 10% in AD30). In accordance with the literature,9 13 extrapyramidal signs were the cardinal features in patients with DLB. Parkinsonism was rarely found in patients with AD and those with CJD, but was present in 58% of patients with DLB. Although described also in 6% of patients with DLB in the literature,9 13 we found choreoathetoid or dystonic movements exclusively in patients with CJD. Clinical signs particularly common in CJD were ataxia and visual disturbances. A differentiation of visual disturbances from visual hallucinations was especially helpful. Although visual disturbances were found exclusively in CJD, visual hallucinations were present in all three dementias. As there are reports from non-CJD dementia syndromes which show predominantly visual impairments, this should be further investigated.31

Although the clinical course was more rapid and myoclonus was more common than generally, our patients with DLB showed the cardinal features of DLB5 (fig 3). Neuroleptic hypersensitivity, a complication in DLB, was not described in any of the patients by the treating physicians. Looking for the clinical details in our patients with DLB, nine of them received neuroleptic medication (median 2 months before death). In six of them, further clinical deterioration and death (median 1 month later) could be consistent with neuroleptic hypersensitivity as described in the literature.18 In three patients with DLB, no hypersensitivity to neuroleptic drugs was found, even with hindsight. Both factors, the lack of hypersensitivity in some patients and no clear correlation of clinical deterioration with administration of neuroleptic drugs, could have contributed to missing the clinical diagnosis of DLB.

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Figure 3

Clinical overlap between CJD, AD, and DLB. *See materials and methods for definition.

Using the diagnostic criteria for PSWCs proposed by Steinhoffet al,19 20 we found EEGs typical of CJD in 56% of patients with CJD, which is slightly less than previously reported.19 In five patients with AD and one patient with DLB, EEG was indistinguishable from typical CJD findings (fig 1 A and B). In four additional patients with AD and two patients with DLB, EEG was considered by notifying hospitals to be compatible with CJD, but these EEGs did not correspond to the established criteria. The high frequency of false positive EEGs is most probably due to study design: demented patients are often referred due to “CJD-like” EEG. In the literature there are reports on periodic sharp wave complexes in single cases of AD11 12 and in two cases of DLB.13 32 “Pseudoperiodicity” in EEG is reported to be more often found in patients with DLB.33

Analysis of CSF16 yielded false positive results for 14–3–3 protein and NSE in one patient with AD and false positive 14–3–3 with normal NSE in another patient with AD. An explanation for the first patient could be an epileptic seizure 4 days before taking the CSF. In the five patients with DLB tested, 14–3–3 was negative and NSE was within the normal range. Negative findings for protein 14–3–3 and NSE in the CSF have also been found in five patients with DLB in another laboratory (Aksamit AJ, personal communication and Aksamit et al 34).

According to Parchi et al,35 in sporadic CJD disease different subtypes exist. As described in detail by Zerr et al,36 the typical clinical phenotype with rapidly progressive dementia, myoclonus and typical EEG and CSF findings is present in about 70% of patients with CJD. In 10% of cases of CJD, disease duration is longer and patients often show extrapyramidal signs (MV2 subtype35 37). In these patients EEG does not show CJD typical PSWCs and testing for protein 14–3–3 yields inconsistant results.36 The patients with MV2 and CJD could thus be missed or mistaken as a non-CJD neurodegenerative disorder, especially DLB. By contrast with AD or DLB, the patients with MV2 and CJD often exhibit ataxia as well as extrapyramidal features. Magnetic resonance imaging showing CJD typical findings in patients with MV238 could also help in the differential diagnosis. Due to lack of material no MR scans were described in this study.

Testing overlap in classification criteria (fig 2), we showed that “probable” CJD was misdiagnosed in six patients with the combination of limb rigidity, myoclonus, and false positive EEGs or CSF data. Classification of all patients according to AD criteria showed also that six patients with CJD and seven patients with DLB met criteria for “probable” AD. Comparable series on patients with DLB reported clinical criteria for “probable” AD in 15% and for “possible” AD in 50% of cases.7 In our study, DLB criteria specifically identified 84% of patients with DLB and falsely classified 16% of patients with CJD and 11% of patients with AD as having DLB.

Although our patients with DLB showed the major clinical signs of DLB (table 2), this disease was not mentioned as a clinical diagnosis in any of our patients. This accords with general findings that DLB escapes diagnosis in up to 66% of cases during a lifetime,8 probably because it is still quite unknown to the clinicians and specific technical examinations for DLB are lacking.

In summary, in patients with rapidly progressive dementia and focal neurological signs, CJD should be the primary diagnosis, especially if EEG shows periodic sharp wave complexes or if the 14–3–3 protein is detectable in CSF (fig 4). Ataxia, visual disturbances, and hyperkinetic limb movements are strong hints for CJD. In a patient with the triad dementia, myoclonus, and rigidity with or without EEG changes, the history should be thoroughly reinvestigated to exclude the possibility that the current condition is the end state of a dementia disorder with a longer duration. In the second case, AD should be considered. A suspicion of DLB should be raised, if an akinetic rigid parkinsonism or fluctuations in cognition are present.

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Figure 4

Diagnostic pattern in the differential diagnosis of patients with the triad dementia, myoclonus, and rigidity.