Spinal dural arteriovenous fistula: delay to radiological diagnosis and sources of radiological error

AIM

To highlight the magnetic resonance imaging (MRI) signs associated with spinal dural arteriovenous fistula (SDAVF) through categorisation of sources of radiological error and investigation of the delay to radiological diagnosis.

MATERIAL AND METHODS

This was a retrospective, observational study of cases referred to a neuroscience centre over 11 years. All patients who underwent spinal digital subtraction angiography (DSA) with a subsequent diagnosis of SDAVF were identified. Prior imaging was reviewed and compared with the formal reports issued.

RESULTS

Thirty-seven patients with SDAVF were initially imaged in seven institutions. Radiological abnormalities including intradural vessels (37/37, 100%), cord T2 signal change (34/37, 91.9%), and cord expansion (26/37, 70.2%) were present on prior MRI. These signs were not recognised in 22/37 (59.5%), 7/34 (20.5%), and 15/26 (57.7%) of cases, respectively. Increased T2 signal in the cord was the most commonly identified sign (27/34; 79.4%), but prompted either no diagnosis (7/34; 20.5%) or differential diagnoses including ischaemic, inflammatory, or neoplastic aetiologies or a syrinx in 11/34 (32.4%). An appropriate diagnosis was made on initial MRI in 15 patients (40.5%). The time from initial imaging to diagnosis was significantly delayed for those patients who did not have an arteriovenous vascular aetiology included in the initial differential diagnosis (281 (423.3) days versus 22 (15.7) days, p=0.03).

CONCLUSION

SDAVF have imaging features that are frequently missed or misinterpreted. This results in a significant delay to definitive diagnosis and therefore treatment.

First-line atypical antipsychotics for schizophrenia are appropriate – with psychosocial interventions

Conventional antipsychotics, historically the mainstay of schizophrenia treatment, were ineffective in many patients, at least 30% fitting treatment-resistance criteria (Kane & Lieberman, 1987). All had the same mechanism of action: none was any more effective in the individual than any other. Therapeutic nihilism accepted poorly controlled positive symptoms and disabling negative symptoms: nearly all patients suffered side-effects (Barnes & Edwards, 1993), particularly extrapyramidal side-effects (EPS) and hyperprolactinaemia. Conventional antipsychotics raise prolactin to a range associated with sexual dysfunction or even macroprolactinoma: effects in men include erectile dysfunction and hypospermatogenesis; in women, galactorrhoea, oligo- or amenorrhoea, hirsutism and increased risk of osteoporosis. In both men and women there is loss of libido, and a link between hyperprolactinaemia and weight gain.

Endovascular treatment of 300 consecutive middle cerebral artery aneurysms: clinical and radiologic outcomes

BACKGROUND AND PURPOSE

There is controversy as to the best mode of treating MCA aneurysms. We report the results of a large endovascular series of patients treated at our center.

MATERIALS AND METHODS

This study was a retrospective analysis of a prospectively acquired data base. All patients with saccular MCA aneurysms treated between November 1996 and June 2012 were included. World Federation of Neurosurgical Societies grade, aneurysm site, size, and aneurysm neck size were recorded, along with clinical outcome assessed with the Glasgow Outcome Scale and radiographic occlusion assessed with the Raymond classification at 6 months and 2.5 years.

RESULTS

A total of 295 patients with 300 MCA aneurysms were treated including 244 ruptured aneurysms (80.7%). The technical failure rate was 4.3% (13 patients). Complete occlusion or neck remnant was achieved in 264 (91.4%). Complications included rupture in 15 patients (5%), thromboembolism in 17 patients (5.7%), and early rebleeding in 3 patients (1%). Overall permanent procedural-related morbidity and mortality were seen in 12 patients (7.8%). Of the ruptured aneurysms, 189 (79.4%) had a favorable clinical outcome (Glasgow Outcome Scale score, 4-5). A total of 33 patients (13.6%) died. On initial angiographic follow-up, aneurysm remnant was seen in 18 aneurysms (8.1%). A total of 13 patients (4.3%) were re-treated.

CONCLUSIONS

Our experience demonstrates that endovascular treatment of MCA aneurysms has an acceptable safety profile with low rates of technical failure and re-treatment. Therefore, coiling is acceptable as the primary treatment of MCA aneurysms.

Retained and fractured microcatheter: a cause of transient ischaemic attacks: endovascular management using carotid stents

A retained microcatheter is a rare complication of endovascular treatment of cerebral aneurysms. We describe such a case that was complicated by delayed microcatheter fracture within the internal carotid artery and subsequent thrombo-embolism resulting in transient ischaemic attacks. We also describe endovascular management of this complication through the use of several carotid stents.

Endovascular therapy for acute basilar artery occlusion: a review of the literature

Basilar artery occlusion is an infrequent form of acute stroke; clinical outcomes are heterogeneous, but the condition can be fatal. There is a lack of randomized controlled trial data in this field. Case series suggest that patients who are recanalized have much better outcomes than those who are not, and it is generally accepted that intra-arterial techniques achieve high rates of recanalization. Controversially, several studies, including a meta-analysis and registry-based investigation, that have compared intravenous thrombolysis (IVT) and intra-arterial treatment suggest similar outcomes. However, there are many potential sources of bias in each of these studies, precluding a firm conclusion. Indeed, there are many confounding factors that can influence the outcome including severity of presentation, site of occlusion, clot load, degree of collateral flow, timing of therapy, agent used for recanalization and dose of thrombolytic agent. Additionally, pretreatment infarct core imaging using diffusion-weighted imaging and the posterior circulation Acute Stroke Prognosis Early CT Score (pc-ASPECTS) scoring systems have been shown to predict outcome and therefore may be useful in selecting patients for aggressive therapy. Protocols combining intravenous agents such as glycoprotein IIb/IIIa receptor antagonists or thombolytics agents with intra-arterial techniques ('bridging' therapy) have shown encouraging improvements in neurological outcome and survival. Furthermore, initial case series describing the use of mechanical clot extraction devices or aspiration catheters suggest high rates of recanalization. What would be useful is a randomized trial comparing IVT, endovascular approaches and a combined IVT/endovascular approach. However, the small numbers of patients and multiple confounding factors are barriers to the development of such a trial.

Coarse pleural calcification in a mesothelioma patient raises the possibility of a rare tumour subtype: osteoblastic sarcomatoid mesothelioma

It is often suggested that calcification seen in association with pleural thickening implies benign disease. However, we present a case of a patient presenting with coarse pleural calcification associated with a pleural effusion and thickening, which following biopsy was shown to represent osteoblastic sarcomatoid mesothelioma. We describe the imaging features associated with this and differentiate these findings from those seen with benign pleural calcification. Similarities are drawn to other rare cases described in the literature.

Multiphase multidetector CT in the diagnosis of haemobilia: a potentially catastrophic ruptured hepatic artery aneurysm complicating the treatment of a patient with locally advanced rectal cancer

Acute haemobilia is an unusual and potentially catastrophic cause of gastrointestinal bleeding. We describe such a case presenting as a rare complication of a hepatic artery aneurysm following the development and successful treatment of subacute bacterial endocarditis during a radical downstaging chemoradiotherapy regime for locally advanced rectal cancer. We suggest that multiphase multidetector-row CT can have an important role in the diagnosis of acute haemobilia and discuss imaging findings associated with the condition. This case raises awareness of benign conditions mimicking malignancy in oncological patients and reinforces the importance of reviewing historical imaging.

Relationship between estrogen and schizophrenia

There is a wealth of historical and circumstantial evidence to suggest that female patients with schizophrenia may suffer from a deficit in estrogenic function. The prolactin-inducing properties of most antipsychotic drugs, and subsequent negative feedback on estrogen levels, is in keeping with this. The functions of estrogen, its complex receptor organization and its numerous actions are the focus of ongoing research activity. Of particular interest are its neuroprotective properties, particularly with regard to cognitive impairment, and its involvement with neurotransmitter systems, which are the substrate for psychotropic drugs. Estrogen has now been used as an adjunct to standard antipsychotic medication in quite a few studies of female schizophrenia patients. However, most of these are not double-blind, randomized, controlled trials. Only two relatively small double-blind, randomized clinical trials returned positive results: one long-term study that selected for hypoestrogenism reported negative findings. Furthermore, recent evidence of the risks of long-term hormone replacement therapy is of concern. The advent of specific estrogen receptor modulators, which may avoid excess risks of cancer and cardiovascular events, will have little to add to schizophrenia treatment if estrogen is, essentially, devoid of any specific antipsychotic or adjuvant mechanism of action relevant to the pathophysiology of this disorder.

Fear of venepuncture as a barrier to testing for blood-borne infection and use of an oral fluid test as an alternative to venepuncture in a genitourinary medicine clinic

OBJECTIVE

A survey of 505 consecutive patients attending a UK genitourinary medicine clinic (GUM) included a psychometric tool to compute a fear of venepuncture (FOV) score, responses to the offer of venepuncture and to alternative testing.

METHOD

An oral fluid test (OFT) was available to test for blood-borne infection (BBI). Completed fear scores were provided by 299 (59%) patients routinely offered venepuncture, of whom 72 (24%) who did not have venepuncture had higher fear scores compared with 227 (76%) who had venepuncture (p<0.001).

RESULTS

Both FOV and female sex were independent predictors of not having venepuncture.

CONCLUSIONS

FOV is an important barrier to uptake of venepuncture. FOV may not always be recognised by health carers. OFT is an acceptable alternative test for some patients with needle aversion who decline venepuncture.

A longitudinal analysis of memory in patients with schizophrenia

Memory deficits are widely reported in patients with schizophrenia, but uncertainties remain about the extent and the longitudinal course of these deficits. Twenty-eight patients with a DSM-IV diagnosis of schizophrenia were tested on multiple aspects of memory at baseline, 9- and 18-month follow-up. Measures included: digit span, the Rivermead Behavioural Memory test (RBMT) battery, the Graded Naming Test (GNT) and several computerized memory tests from the Cambridge Automated Neuropsychological Testing Battery (CANTAB). A group of healthy controls (N=17) was tested on the CANTAB battery at baseline and 9-month follow up. The patients performed significantly poorer than controls on all CANTAB measures; however, there was no difference in change between groups over a 9-month period. Within-group patient comparisons revealed that symptoms reduced significantly over the study period, but had no association with memory. Significant improvements were observed for patients on two verbal memory tasks: the GNT and digit span, but not on any other measure. Interestingly, these were the only two tests on which patients were within normal limits at baseline. This study shows that patients with schizophrenia have deficits in multiple aspects of memory which remain stable over long periods of time. In addition, patients showed a tendency to improve on memory tasks which contained a verbal component.

Somatic treatment of psychotic depression: review and recommendations for practice

The diagnosis, classification, and course of psychotic major depression (PMD) is considered with regard to its status as a distinct syndrome. Several factors, especially biological markers, suggest, although as yet do not confirm, that PMD is distinct from nonpsychotic major depression (NPMD), particularly for the purposes of treatment. This article provides a critical review of somatic treatments for PMD, with attention to problems of inadequate treatment, as well as underused and more recently introduced treatments. The somatic treatment options reviewed include (1) combined antidepressant (AD) and antipsychotic (AP) therapy with tricyclic antidepressants (TCAs) and typical APs; (2) electroconvulsive therapy (ECT); (3) amoxapine; (4) selective serotonin reuptake inhibitors (SSRIs), alone and in combination; (5) several atypical APs, alone and in combination; (6) mood stabilizers and anticonvulsants; and (7) some experimental treatments and surgery. A comprehensive treatment algorithm (heuristic) is presented, which draws on some previous guidelines and the critical review. This heuristic is conservative in its aims, but forward-looking in its recommendations. The status of the TCA plus typical AP regime is challenged as the default first-line treatment, and preferable alternatives are discussed. ECT has been shown to be at least as effective in short-term treatment and should be considered more frequently, especially in severe presentations and as a maintenance treatment. Some single compounds should be considered as first-line monotherapies in less severe cases. For cases in which combined AD+AP regimes are instituted, SSRIs and atypical APs should be used before older classes of drugs are considered. These recommendations aim to minimize the number of treatments used and unwanted effects experienced.

Lexical knowledge degradation in schizophrenia

This study documents a severe picture naming impairment in a series of 22 chronically hospitalised schizophrenics. The pattern and level of naming impairment were comparable in degree and type to that seen neurological patients with left hemisphere lesions. This deficit was further examined to determine whether it conformed to a disorder affecting access to the lexical representations or some degradation of the stored representations themselves. Patient naming was examined twice (18months apart) for evidence of consistency and for word frequency effects. The pattern of individual patient performance on these criteria showed that the majority had storage disorders; access disorders alone occurred in only a small minority of patients. A subset of 11 of the same patients that were tested on three occasions (across 30months) showed the same pattern but further indicated that when access problems are present, they reflect difficulty with deliberate, rather than automatic, access to the lexicon.

Reduced dendritic spine density on cerebral cortical pyramidal neurons in schizophrenia

OBJECTIVE

A pilot study of the density of dendritic spines on pyramidal neurons in layer III of human temporal and frontal cerebral neocortex in schizophrenia.

METHODS

Postmortem material from a group of eight prospectively diagnosed schizophrenic patients, five archive schizophrenic patients, 11 non-schizophrenic controls, and one patient with schizophrenia-like psychosis, thought to be due to substance misuse, was impregnated with a rapid Golgi method. Spines were counted on the dendrites of pyramidal neurons in temporal and frontal association areas, of which the soma was in layer III (which take part in corticocortical connectivity) and which met strict criteria for impregnation quality. Altogether 25 blocks were studied in the schizophrenic group and 21 in the controls. If more than one block was examined from a single area, the counts for that area were averaged. All measurements were made blind: diagnoses were only disclosed by a third party after measurements were completed. Possible confounding affects of coexisting Alzheimer's disease were taken into account, as were the effects of age at death and postmortem interval.

RESULTS

There was a significant (p<0.001) reduction in the numerical density of spines in schizophrenia (276/mm in control temporal cortex and 112/mm in schizophrenic patients, and 299 and 101 respectively in the frontal cortex). An analysis of variance, taking out effects of age at death and postmortem interval, which might have explained the low spine density for some of the schizophrenic patients, did not affect the significance of the results.

CONCLUSION

The results support the concept of there being a defect in the fine structure of dendrites of pyramidal neurons, involving loss of spines, in schizophrenia and may help to explain the loss of cortical volume without loss of neurons in this condition, although the effect of neuroleptic drugs cannot be ruled out.

Spatial dynamics and critical patch size of annual plant populations

Critical patch size is the minimum habitat size required for population persistence. The critical patch size of an annual plant population residing in a finite homogeneous habitat, using an integro-difference equation model is considered and this is found to be dependent on the basic population growth rate and dispersal characteristics. General analytical and numerical methods for the calculation of the critical patch size are presented with the inclusion of a simple new approximation technique. These methods are illustrated in the context of a species dispersing seeds on a Gaussian distribution. The approach is extended to incorporate a persistent seed-bank. Where the dispersion of seeds entering the seed-bank and those giving rise to adult plants is identical, the possession of a seed-bank influences the critical patch size through a scaling of the basic population growth rate. The wider implications of the approach are discussed in the context of metapopulation dynamics.Copyright 1998 Academic Press Limited

Cognitive function in schizophrenia--do neuroleptics make a difference?

Valid cognitive deficits in schizophrenia are now well characterised: general poor performance with disproportionate deficits in aspects of memory and executive function. Symptomatology, motivation, institutionalization, etc. cannot explain these deficits, which are of considerable importance for both the testing of theoretical models of schizophrenia and the determination of patients' functional outcome. The receptor blocking properties of neuroleptic treatments afford them the potential for interacting with monoaminergic, indoleaminergic, and cholinergic arousal systems in the brain and, hence, for modifying cognitive processes. However, the effects of conventional neuroleptics on cognition in schizophrenia are minor according to numerous studies. Atypical neuroleptics may, owing to their novel mechanisms of action, have the capacity to remediate cognitive impairment in schizophrenia: there is some evidence that clozapine has a "cognitive sparing" effect, but further research is needed in this area, particularly with other new drugs. Future studies should employ more appropriate methodology, particularly in terms of psychological/neurophysiological sophistication, patient evaluation, and applicability to real life, and should be hypothesis driven rather than purely empirical.

Semantic memory is impaired in schizophrenia

Memory is emerging as a key area of neuropsychological deficit in schizophrenia, with evidence suggesting that the impairment is restricted to long-term memory. Semantic memory, the component of long-term memory containing stored representations of the meanings of words and knowledge about the world, was examined in 46 schizophrenic patients and 40 normal controls using a recently devised battery of tests. Evidence of semantic memory impairment was found which was wide ranging and substantial; in some cases it approached the levels seen in a group of 22 patients with mild-to-moderate Alzheimer's disease. Both group analysis and a more detailed examination of two single cases suggested that semantic memory impairment represents a disproportionate and possibly specific neuropsychological deficit in schizophrenia.

Memory in schizophrenia: what is impaired and what is preserved?

This study assesses the pattern of long-term memory performance in a sample of 12 schizophrenic patients who were selected on the basis of showing a memory deficit in the absence of gross overall intellectual impairment. When compared with 12 control subjects matched for age, sex and estimated premorbid IQ, presence of an episodic memory deficit was confirmed for both prose recall and forced-choice word and face recognition. Semantic memory was assessed using the sentence verification task developed by Collins and Quillian, an unpaced category judgement task, and the Mill Hill Vocabulary Scale. The schizophrenic patients were slower on sentence verification and they made significantly more errors in all three tasks. Procedural tasks included pursuit rotor performance, speed of repeatedly assembling a jigsaw puzzle and rate of improvement in reading transformed script. Here, while the schizophrenic patients showed poor overall performance on the pursuit rotor and jigsaw learning, their rate of learning on all three procedural tasks was comparable with that of the controls. When examined on two implicit memory tasks involving biasing of spelling of homophones and word stem completion, the patients showed a normal degree of priming in both. Implications for the nature of the memory deficit in schizophrenia are discussed.

Carryover effects on the clonal growth of the grass Holcus lanatus L

The effects of clipping and daylength treatments and their carryover effects on the clonal growth of the perennial grass Holcus lanatus L. were investigated. Plants from ten clones were grown in six combinations of two daylength and three clipping treatments. Both clipping and low daylength reduced the tillering rate of all the clones but the clones differed in their degree of response to these treatments. After eight weeks, the treatments were discontinued and plants were grown in a common environment for seven weeks. Four-week-old tillers from the plants were repotted and grown in a common environment to examine the possibility of 'carryover' effects of the parental environments. After 8 wk of growth, there were main and interaction carryover effects of daylength and clipping on the tillering rates, biomass and tiller extension rates of the plants, which, however, differed greatly among clones. These differences among clones in both direct and carryover treatment effects, on clonal growth, indicate how the effects of many different environmental variables may interact to produce an environment that is highly heterogeneous in space and time, influencing the coexistence of genotypes and species.

Phenomenology. Its place in schizophrenia research

In some quarters schizophrenia has gained the reputation of a graveyard of research. Few findings stand the test of time, most of the pieces of this particular jigsaw seem to be missing, and it is not easy to make sense of those that are available. Even ‘hard’ scientific findings fail to be replicated, an example being the status of D2receptors in drug-naive schizophrenics (Wonget al, 1986; Fardeet al, 1987).

Memory impairment in schizophrenia: its extent, affiliations and neuropsychological character

In a sample of 60 schizophrenic patients encompassing all grades of severity and chronicity memory impairment was found to be prevalent, often substantial, and disproportionate to the overall level of intellectual impairment. The deficits were not easily attributable to poor cooperation, attention or motivation; nor were they related to neuroleptic or anticholinergic medication. Memory impairment was significantly associated with severity and chronicity of illness and also with negative symptoms and formal thought disorder. There was evidence from the sample as a whole, and from a more detailed examination of five patients with relatively isolated deficits, that schizophrenic memory impairment conformed to the pattern seen in the classical amnesic syndrome. Additionally, there was preliminary evidence for a marked deficit in semantic memory.

Motor, volitional and behavioural disorders in schizophrenia. 1: Assessment using the Modified Rogers Scale

The assessment of catatonic symptoms, unlike that of other schizophrenia symptoms, has not acquired accuracy and phenomenological rigour, and their distinction from extrapyramidal side-effects is not always easy. The Modified Rogers Scale can rate abnormalities in movement, volition, speech, and overall behaviour in schizophrenia. It is detailed, reliable and valid, and permits the isolation of a score for non-extrapyramidal and hence presumably catatonic phenomena.

Motor, volitional and behavioural disorders in schizophrenia. 2: The 'conflict of paradigms' hypothesis

An alternative to the conventional separation of extrapyramidal and catatonic symptoms exists in the 'conflict of paradigms' hypothesis, which proposes that there is a relative rather than absolute distinction between the two. The hypothesis predicts that a clinical association should exist between extrapyramidal and catatonic symptoms in schizophrenia. After rating 75 schizophrenic patients, a highly significant correlation between scores on the two classes of disorder was indeed found. This was composed of separate correlations between tardive dyskinesia and 'positive' catatonic phenomena, and Parkinsonism and 'negative' catatonic phenomena. The associations were not easily attributable to confounding factors and they were supported by factor analysis.

Amnesic syndrome in schizophrenia

Memory impairment is not usually considered to form part of the clinical picture of schizophrenia, except perhaps in severely deteriorated patients. In a survey of 60 patients encompassing all grades of severity and chronicity poor memory performance was found to be common, sometimes substantial, and disproportionately pronounced compared to the degree of general intellectual impairment. Although associated with severity and chronicity of illness, impaired memory was by no means confined to old, institutionalized, or markedly deteriorated patients. The pattern of deficit appeared to resemble that of the classic amnesic syndrome rather than that seen in Alzheimer-type dementia.

The positive:negative dichotomy in schizophrenia

Two studies are reported. In the first, of 62 schizophrenic patients, no correlation between negative symptom scores (rated blindly) and any measure of positive symptoms was found. This independence was confirmed by factor and cluster analyses, which left the question of a third 'disorganisation' class of schizophrenic symptoms open. In the second study, of 80 patients, formal thought disorder separated unequivocally into 'positive formal thought disorder' and 'alogia' syndromes on the basis of correlations with positive and negative symptoms. Catatonic motor disorder also showed evidence of a corresponding positive: negative division, although this only emerged when severity or chronicity of illness was controlled for. Cognitive impairment showed a broad range of affiliations and its particular correlation with negative symptoms was perhaps artefactual.

Detecting aberrant strains in bacterial groups as an aid to constructing databases for computer identification

Computer assisted identification systems require that databases on the test results of the species are of high quality. One reason for poor quality is the inadvertent inclusion of strains that do not belong to a taxon; this can readily occur in groups where ancillary criteria (e.g. serology) are not available. A possible strategy is to exclude strains that are very atypical in their properties, i.e. that are very outlying, provided an objective criterion can be used. A computer program, OUTLIER, for the detection of outlying strains in bacterial clusters was evaluated. A brief description of the theory and operation of the program is given. The program uses as an objective criterion the degree to which the strain data fits a chi-square. This allows easy identification of aberrant strains that should be excluded in constructing a database. The program utilizes 1.0 data and calculations are based upon a choice of one of four identification coefficients. The relative merits of these four coefficients were examined for eight sets of bacterial data. Two of the coefficients, -log10 Willcox likelihood and Taxonomic distance squared appear to show little significant differences and we recommend these for routine work, with the first being the more useful. The Pattern distance squared was useful in indicating where atypical strains may be metabolically less active or slow-growing members of a cluster rather than true outliers. The Variance-weighted Taxonomic distance squared behaved anomalously and we do not recommend it.

New probability matrices for identification of Streptomyces

The character state data obtained for clusters defined in a previous phenetic classification were used to construct two probabilistic matrices for Streptomyces species. These superseded an original published identification matrix by exclusion of other genera and the inclusion of more Streptomyces species. Separate matrices were constructed for major and minor clusters. The minimum number of diagnostic characters for each matrix was selected by computer programs for determination of character separation indices (CHARSEP) and a selection of group diagnostic properties (DIACHAR). The resulting matrices consisted of 26 phena x 50 characters (major clusters) and 28 phena x 39 characters (minor clusters). Cluster overlap (OVERMAT program) was small in both matrices. Identification scores were used to evaluate both matrices. The theoretically best scores for the most typical example of each cluster (MOSTTYP program) were all satisfactory. Input of test data for randomly selected cluster representatives resulted in correct identification with high scores. The major cluster matrix was shown to be practically sound by its application to 35 unknown soil isolates, 77% of which were clearly identified. The minor cluster matrix provides tentative probabilistic identifications as the small number of strains in each cluster reduces its ability to withstand test variation. A diagnostic table for single-membered clusters, constructed using the CHARSEP and DIACHAR programs, was also produced.

A probability matrix for identification of some Streptomycetes

The character state data obtained for clusters defined at the 77.5% SSM similarity level in the phenetic numerical classification described by Williams et al. (1983) were used to construct a probabilistic identification matrix. The 23 phena included were the major clusters (19 Streptomyces, 2 Streptoverticillium and 'Nocardia' mediterranea) and one minor cluster (Streptomyces fradiae). The characters most diagnostic for these clusters were selected using Sneath's CHARSEP and DIACHAR programs. The resulting matrix consisted of 41 characters x 23 phena. Identification scores, determined by Sneath's MATIDEN program were used to evaluate the matrix. Theoretical assessment was achieved by determination of the cluster overlap (OVERMAT), the identification scores for the Hypothetical Medium Organism of each cluster (MOSTTYP), and the scores for randomly selected cluster representatives using the classification data of Williams et al. (1983). The matrix was evaluated practically by the independent re-determination of the characters for the same cluster representatives, which also provided a measure of test error. Finally it was used to identify unknown isolates from a range of habitats. The results showed that the matrix was theoretically sound. Test error was within acceptable limits and did not distort identifications. Of the unknown isolates, 80% were clearly identified with a cluster. It is suggested that the matrix could form the basis for a more objective identification and grouping of the large number of Streptomyces species which have been described.