The diagnostic performance (compared with clinician diagnosis) of questionnaires for TIA vary with the population tested. The Questionnaire to Verify Stroke Free Status (QVSFS) has been validated in stroke and general medical out-patient clinics with varying reports of 96% negative predictive value (NPV), 71% positive predictive value (PPV) (194) and 100% NPV and 36% PPV respectively (195). A six item derivative of the QVSFS which only contains questions about clinical symptoms was used in Veterans Affairs clinics in the US
33 with reported sensitivity of 82% and specificity of 62% in a population of patients with a prevalence of stroke of 50%, which equates to a PPV of 68% and an NPV of 78% (196). These results suggest that a rule out function is more reliable than making positive diagnoses.
In the Asymptomatic Carotid Atherosclerosis Study (ACAS), an algorithm for TIA diagnosis based on questionnaire responses in a selected population of patients presenting with TIA or stroke like symptoms, had an 88% sensitivity and 71% specificity for cerebrovascular
diagnoses compared with an expert panel for patients reporting stroke-like episodes within the trial (197).
Reliance on questionnaires may result in a bias towards diagnosing anterior rather than posterior events. A diagnostic algorithm in the Atherosclerosis Risk in Communities (ARIC) study was more likely to diagnose self reported symptoms as TIA if they were anterior rather than posterior circulation (198). Nevertheless, the ARIC algorithm estimated a community prevalence of 5-6% of TIA/Stroke (199) and there is face validity to the algorithm in that those diagnosed with TIA had higher risk of stroke over a subsequent 11 year follow up period (200).
A TIA questionnaire by Wilkinson in 10,000 US care home residents showed that 6.4% had suggestive symptoms of TIA and 15.4% had possible symptoms but in a sample of 1700 respondents, the PPV of the questionnaire for TIA diagnosis by a neurologist was 7% (201). A nurse administered version of this questionnaire in a population of patients referred after suspected TIA to a UK hospital clinic had a positive predictive value of 66% for combined TIA and stroke diagnoses reflecting the much higher prevalence for TIA and stroke compared with the care home population (202).
2.9.4 GPs’ ability to diagnose TIA and stroke – responses to case vignettes
There are very few reports of studies that assess how GPs diagnose cerebrovascular events. Questionnaire studies using case vignettes have been used to test GPs’ recognition of TIA and subsequent management either with free text without cueing TIA, or with a restricted set of diagnoses which automatically cues TIA as a diagnostic possibility. All studies have used artificially constructed cases and are restricted to anterior circulation presentations.
Explicitly varying a parameter in case vignettes has been used to test GPs’ ability to suspect TIA and the influences on decisions to refer for assessment. Quik-van Milligen constructed five matched pairs of cases, varying one aspect of the history in each pair. Anterior
34 circulation symptoms were used, which was justified by the authors from the low prevalence of posterior circulation presentations (203). The five history parameters varied were; age (dichotomised to <65 or > 65), single vs multiple episodes, history of non-specific symptoms vs no history, brief (few minutes) vs longer (20-24 hrs) duration and cortical vs retinal pattern of symptoms. The cases were mixed with ten distractor cases (five had neurological disease and five had infectious disease) and sent to Dutch GPs, with 376 responding (59% of the sample). The authors state that cases were placed in a random order, although it is not clear if the order was at random for each questionnaire i.e. individual questionnaires had a
different presentation order. The GPs were asked “What is your diagnosis?” with free text response and “What are you going to do?” with a restricted choice of suggested options including reassurance, investigations, new prescriptions and referral.
They found that GPs were more likely to diagnose TIA for cortical rather than retinal patterns of symptoms, younger rather than older age (contrary to the prevalence rate (16)), recurrent rather than single attacks, and an absence of non-specific symptoms. Referral to a
neurologist was more likely for cortical rather than retinal symptom patterns, although overall there were more referrals to specialists in the retinal vignettes if ophthalmology referrals are included. However this study was reported in 1992 and was therefore carried out before guidelines and national strategies were in place for optimal evidence-based management for TIA.
Permutations in multiple parameters within a single case vignette have been used to assess the features that influence diagnosis and referral for one presentation of anterior circulation TIA - transient monocular visual disturbance (204). In this study of the responses of 866 Dutch GPs (54% of their sample), one TIA case was used from a bank of 16 cases created from two possibilities for each of four characteristics; blurring of vision vs complete visual loss, all of the visual field affected vs part of the visual field, duration of a few minutes vs a few hours and the patient did or did not report covering each eye in turn during the episode. The age was kept at 56 years, a suggested ‘neutral’ age which would encourage the GPs to focus on clinical presentation as the basis for decision making. Only one of the possible 16 cases was sent to each GP with three distractor cases included (lumbosacral radiculopathy, syncope and polyneuropathy).
The range of GP responses were from fixed lists for diagnosis and for management. The likelihood of each diagnosis of retinal migraine, optic neuritis, glaucoma, retinal detachment, amaurosis fugax, cortical TIA or other was rated visually by placing a mark on a line from ‘very improbable’ to ‘highly probable’. Offered management options included reassurance, medication (free text choice) and referral (specifying routine or urgent and to whom) and the
35 GPs rated how strongly they agreed with each suggested course of action by marking a line from ‘agree’ to ‘not agree’. Amaurosis was considered more likely for brief, visual loss (rather than blurring) affecting the complete field of vision. Performance of a cover test by the
patient did not affect the perceived likelihood of the diagnosis. Of those diagnosing
amaurosis or cortical TIA, 72% and 64% respectively recommended specialist referral but again, this study was reported in 1999 before recent advances in evidence based benefit, and timing, of treatment.
A study of Polish GPs’ examined whether age or affected territory (within the carotid distribution) influenced correct diagnosis or referral decisions using six carotid territory TIA vignettes (205). The study authors again justified the restriction to the anterior circulation by a low prevalence of posterior circulation symptoms. The three pairs of vignettes consisted of firstly keeping age constant but varying cortical or retinal ischaemia, the second pair
consisted of retinal symptoms with age variation (above and below 65 years) and the third pair consisted of cortical symptoms with similar age variation. Each case also contained information about previous episodes and a history of non-specific symptoms, similar to the Quik-van Milligen study (203). Diagnostic responses were free text but management responses were semi-structured with GPs indicating whether they would perform additional tests, initiate medication or refer for specialist assessment.
In 89 respondents (89% of the sample), correct diagnosis of both cortical TIA and amaurosis was less likely with recurrent episodes and a history of non-specific symptoms. For the cases without a history of non-specific symptoms and without previous episodes, younger age reduced the likelihood of a correct diagnosis of cortical TIA but age did not affect the correct diagnosis of amaurosis. In general the likelihood of correct diagnosis was higher for cortical TIA than for amaurosis, a similar finding to the Quik-van Milligen study (203). Although they do not present total referrals for each case, age did not affect referral to neurologists after cortical TIA or amaurosis. In the direct comparison between cortical and retinal territory, more patients with cortical symptoms were referred to a neurologist and more patients with retinal symptoms were referred to an ophthalmologist.
2.9.5 Recognition tools for diagnosis of cerebrovascular disease – easier for stroke