most of the schools of medicine of the ancient world considered every single symptom and sign as a separate disease itself . in 1742 , sydenham was the first scientist to clearly formulate the minimum requirements needed to define a clinical condition as a syndrome . in his definition , a syndrome consists of several interrelated symptoms showing a stable , characteristic structure and a peculiar prognosis . furthermore , patients affected by a specific syndrome should share a sufficiently pathognomonic cluster of symptoms that allows clinicians to distinguish them from other patients suffering from different syndromes . such fundamental elements of discontinuity among various syndromes were , at first , better conceptualized by sneath , who introduced the term of " point of rarity  to refer to precise clinical boundaries among disorders , and were later revised by kendell and jablensky , who preferred the concept of  zone of rarity  separating psychiatric syndromes . the idea was that if a syndrome corresponds to a natural entity , than we should find a natural boundary or a discontinuity between this condition and its clinical  neighbours  ; in other terms , mixed conditions can exist , but they have to be less common than the pure syndromal form . several authors [ i.e. 1 ,   2 , 6 ] have investigated whether such a theoretical construct could be applied to the field of mental disorders . in spite of the improvement in this field , the validity of the actual classifications ( icd-10 , dsm - iv - tr ) still remains a matter of debate . although formal criteria to establish the validity of psychiatric diagnoses have been progressively proposed ( i.e. , descriptive features , sociodemographic factors , laboratory markers , exclusion criteria , neurobiologic and genetic validators , prognostic characteristics , level of functional and social disability , response to therapy , statistical deviation from the healthy condition , etc . ) [ 9 - 11 ] , in a clinical framework some of the conditions that are currently classified as psychiatric disorders still appear as vague and confusing ( rather than discrete ) entities . in particular , most of them show weak diagnostic criteria ( low association between diagnostic symptoms and actual diagnosis ) , unspecific manifestations ( poorly pathognomonic symptoms ) , and widespread onset ( high comorbidity ) . according to the mentioned sydenham s definition of syndrome , a first anomaly has to be taken into account : several diagnostic categories changed their criteria in different dsm editions and some of them were abolished , merged with other conditions , or divided into two or more entities . gad was first introduced as a unique diagnosis in the third edition of the dsm ( dsm - iii ) , but it was most often used as a residual diagnosis for individuals who did not meet diagnostic criteria for another anxiety disorder . considering the difficulty to discriminate between gad and other disorders [ 14 - 15 ] , the definition of gad and the associated symptoms were substantially revised in the further edition of dsm . as a consequence , the dsm - iv - tr   considered gad as an independent diagnosis among the anxiety disorders , characterized by  excessive , uncontrollable worry about a variety of topics that occurs more days than not for a period of at least six months  . the worry causes distress and/or functional impairment , and is associated with at least three of the following features : restlessness or feeling keyed up or on edge , being easily fatigued , difficulty concentrating or mind going blank , irritability , muscle tension , and sleep disturbance ( difficulty falling or staying asleep , or restless unsatisfying sleep ) . indeed , four out of the six associated physical symptoms of gad ( i.e. restlessness , fatigue , difficulty concentrating , sleep difficulties , obsessive rumination , somatization ) are also part of the diagnostic criteria for major depressive disorder [ 16 , 17 ] . furthermore , symptoms required for gad diagnosis are also present in other anxiety disorders , as closer overlaps probably exist between gad and panic disorder or social anxiety disorder . in general the nosographic ambiguity - which is related to different psychiatric diagnoses - makes it very hard to define a stable constellation of interrelating symptoms and to characterize a specific population of patients with a specific diagnosis . the uncertain psychopathologic boundary of many psychiatric conditions seems to further move these disorders away from the original definition of discrete syndromes . the psychiatric comorbidity  defined as co - occurrence of two or more psychiatric diagnoses in the same patient  raised a significant concern in the debate on the categorization of psychiatric disorders . the concept of comorbidity was first introduced by feinstein   to denote those cases in which a distinct additional clinical entity occurred during the clinical course of a patient having an index disease . this concept was recently used to indicate not only those cases in which a patient receives both a psychiatric and a general medical diagnosis , but also those cases in which two or more psychiatric diagnoses are present in the same patient . the lack of well - defined and specific symptoms for many disorders and the high rates of gad comorbidity with other anxiety and mood disorders make it difficult for the clinician to perform a reliable differential diagnosis and to correctly identify this condition [ 18 , 21 ] . moreover , neurotic symptoms appear to be more frequent in mixed or associated forms than as parts of pure conditions . again , the high rate for gad comorbidity was considered to challenge the validity of this diagnosis . the different revisions of dsm criteria for gad did not solve the matter of comorbidity , and its high rates of co - occurrence with other anxiety or mood disorder are still widely reported [ 13 , 22 - 27 ] . to support the concerns raised above , we performed further analyses of the data from the sesto fiorentino study , a large community study , which has been described in detail elsewhere . i.e. regardless of the diagnosis : diagnostic categories are built up later , by computerized algorithms . such an approach does not depend on pre - constructed nosological theories , allows the analysis of natural aggregations of symptoms even below their diagnostic cutoff points , permits the comparison of the qualitative and quantitative aspects , and can be useful to investigate specificity of diagnostic symptoms . we evaluated the presence of some common mood and anxiety symptoms across the most represented dsm iv diagnoses ( fig . it is clear that these symptoms occur transversally in a variety of diagnostic categories , with little variations from each other . as far as the gad symptoms are concerned , a further analysis was performed on the data from the sesto fiorentino study : we tested for significant differences in each of the gad symptom reported in fig . these results confirmed that the symptoms which are required for a diagnosis of major depressive episode or generalized anxiety disorder are essentially non - specific . stand alone  , independently of the presence of other symptoms , whereas in the clinical practice the co - occurrence of other symptoms may consistently modify the interpretation of the clinical presentation . suicidal thoughts accompanied by delusions of guilt are considered potentially more dangerous than suicidal ideation plus hystrionic features . the application of the categorical model in psychiatry is likely to be different from the one used in other medical sciences . in general medicine , symptoms are considered either non - specific ( fever or fatigue may be taken as an example ) , or specific ( such as the aspect of blisters in hzv infection ) . in medicine we do not count symptoms in order to make a diagnosis : peritonitis and flu may share some symptoms , for example fever , pallor or fatigue ( non - specific ) , but they can not be used to make up the diagnosis of peritonitis with a comorbid flu , and in any case if a peritonitis is present , none would assign the same value to the symptom  fatigue  and to the one  abdominal guarding exacerbated by moving peritoneum  . dsm - iii and its successors , became universally and uncritically accepted as the ultimate authority on psychopathology and diagnosis . although it represents an undoubted progress for reliability and communication between clinicians and researchers , the price that psychiatry had to pay for these benefits is very high : the diagnostic process lost out in terms of sophistication and specificity . according to andreasen , our data demonstrated that diagnostic criteria include only some characteristic symptoms of a given disorder but they were never intended to provide a comprehensive description . although creating standardized diagnoses that would facilitate research was a major goal , dsm diagnoses are not useful for research because of their lack of validity . since the core features of mental illness were mainly unknown , both the symptom pattern and the prognostic value ( e.g. duration , course and severity ) of psychiatric syndromes were defined arbitrarily and conventionally . many examples can be mentioned to support this idea , ranging from the scarce agreement between dsm / icd classification systems [ 31 , 32 ] to the lack of validity of schizophrenia subtypes   and the problems inherent in the diagnosis of some psychiatric disorders ( i.e. schizoaffective disorder ) [ 34 , 35 ] . therefore , the validity of the present nosology has never been sufficiently demonstrated . on the contrary , the premise that original dsm diagnostic categories are primarily artificial and have no confirmed value of elementary clinical entities , is usually forgotten . this shortness of memory can push psychiatrists to think that dsm / icd diagnoses are natural categorical entities ( a phenomenon that van praag called  nosologomania  ) , thus making them accept unconditionally and uncritically the current classification system and ignore alternative models . many authors believe that this might represent a rather blind approach that may be either dangerous or useless in terms of application in biological and psychopharmacological research . in fact , most of the available scientific studies are actually based on the current arbitrary classification , even if it may not match with the correspondent biological and clinical sources . on the other hand , studies based on the so - called dimensional approach to psychopathology [ 37 - 39 ] show a relative aspecificity of diagnostic categories and provide robust examples of usefulness of reasoning , in terms of symptom clusters . in our opinion , the current nosographic system prevents psychiatry from benefiting of the significant technological progress that has led the rest of medical sciences to important clinical achievements in the last 20 years . in the future , psychiatry will be probably able to find new and more specific markers and instruments [ 40 , 41 ] .
the present article focused on the problem of validity , reliability and specificity of psychiatric diagnoses.the authors moved by the concept of syndrome , defined by sydenham in the 18th century as a constellation of several interrelated symptoms , showing a stable , characteristic structure and a peculiar prognosis , in order to analyse the peculiarity of the current psychiatric nosology . in our opinion , 
 the current nosographic system based on dsm - iv criteria , prevents psychiatry from benefiting of the significant technological progress that has led the rest of medical sciences to important clinical achievements in the last 20 years . 
 the case of generalized anxiety disorder was taken as an example of a disease characterized by unstable diagnostic criteria , high rate of comorbidity and uncertain boundaries . 
 an analysis of the data from the sesto fiorentino study was performed to investigate the presence of common mood and anxiety symptoms across the most represented dsm iv diagnoses , in order to evaluate the specificity of these symptoms.the results supported the hypothesis of a low specificity of these symptoms , suggesting the need for psychiatry to find new and more specific markers and instruments .