A previous review of historical descriptions and interpretations of writer's cramp and other work-related upper limb "overuse" conditions with a special emphasis on writer's cramp has suggested that the workers' symptoms and the findings on physical examination can be explained by peripheral nerve afflictions . The initial interpretations by the ancient authors were that these ailments were peripheral and caused by afflictions of nerves or muscles although it was acknowledged that a psychic vulnerability could also play a role. Towards the end of the 19th century, this perception was gradually changed and the symptoms were assumed to represent dysfunctions in the central nervous system. At that time these conditions were understood as occupational "neuroses" - a term applied at the time when no somatic pathology could be identified. In the beginning of the 20th century these conditions were increasingly regarded as purely psychoneurotic.
The various hypotheses can be seen against the diagnostic challenges in relation to upper limb work-related disorders that clinicians encountered. These difficulties were not only present previously but remain central to the scientific debate and clinical practice, e.g. in relation to the character of arm pain in computer operators. The majority of upper limb patients seen in an occupational context are regarded to be uncovered by consensus diagnostic case definitions  and cannot be diagnosed with a physical standard approach.
This article presents historical case reports and interpretations that attribute symptoms to the sphere of psychiatry, and compares the historical descriptions with current observations and assessments of upper limb pain conditions. The neurological examination of the peripheral nerves is particularly emphasized.
Central nervous dysfunction in vulnerable/nervous workers
In 20th century, many experts perceived work-related "overuse" disorders such as writer's cramp as functional conditions and termed them occupational "neuroses", since no somatic pathology could be identified. Coined by William Cullen in 1769, the term "neurosis" referred to "disorders of sense and motion" caused by a "general affection of the nervous system". Cullen used the term to describe various nervous disorders and symptoms that could not be explained physiologically. The meaning of the term was redefined by Jung and Freud in the early and middle twentieth century. It has continued to be used in psychology and philosophy while neurosis is no longer used as a psychiatric diagnosis.
Gowers, a prominent neurologist towards the end of 19th century, termed writer's cramp and comparable work-related disorders as occupational neuroses understanding by this concept conditions, which according to the existing knowledge lack underlying lesions of the nervous system. He perceived symptoms to be caused by performing repetitive muscle actions, usually related to the patient's work, and regarded excessive writing as the main causal factor because writer's cramp was particularly prevalent among professional writers. He noted, however, that nervousness and anxiety predisposed for the condition, especially when it occurred in people who had not written much. He therefore believed that "a lowered tone" of the nervous system predisposed to the condition. He described most patients as nervous, irritable and sensitive with a psycho-neurotic personality showing signs and symptoms of pathological anxiety. The patients were frequently concerned about work and family issues, and heavy burdens of responsibility and problems relating to the work were other characteristic features . This view was supported by Cassirer and Oppenheim  , who stated that writer's cramp could develop consequent to a dysfunctional nervous system such as with neurasthenia, a neuropathic predisposition, persistent emotions, a functional condition, or an exhaustion neurosis . This understanding persisted, because it was in accordance with the general understanding at the time, namely that these diseases were consequences of a congenital vulnerability of the nervous system, which was influenced by the stress and strain of modern civilization . The occupational "neuroses" were explained by somatic dysfunctions of the central nervous system, which nervous people were more prone to acquire than others  .
Psychological and psychiatric descriptions and interpretations of work-related "overuse" conditions
In 1925, Janet contributed to the debate by arguing that psychasthenic symptoms develop secondary to nervous exhaustion. Janet described a patient with perfectionistic traits who had spasmodic writer's cramp and described the consequences of her promotion with allocation of greater responsibility . Seeing clear links to psychoneurotic conditions with symptoms such as nervous exhaustion, phobia, obsessions, compulsions, hysteria and anxiety, Janet  and Culpin  emphasized that some patients had symptoms under observation only, and that symptoms could occur without excessive writing  . Consequently, they concluded that writer's cramp could not represent a disorder of the central nervous system. Williams who also rejected the previous theories of occupational "neuroses"  attributed the symptoms in writer's cramp to psychodynamic inhibitions - a psychological disharmony in the control of the mechanism in the habitual series of coordinated associations obtained through learning. He emphasized that the neuromuscular system could be unable to perform a specific occupational action but was still able to perform other operations by using the same muscles, nerves and brain areas. Williams attributed the lack of coordination to the influence of mental processes on the work but also pointed out the importance of preventing fatigue and improving the workers' overall health. He regarded prevention as impossible, however, unless the "growth of ideas in the worker's mind" could be avoided .
The psychologist Lucire perceived chronic "overuse" upper limb disorders as of a purely psychogenic character  and found features of both somatization and conversion in these conditions . She rejected the theory that they represented a disorder of muscles, since there is no condition in which muscles become dysfunctional and painful for one activity, but not for another. Excluding an underlying physical damage, Lucire suggested a psychosocial pathogenic model for its development  
The model assumed the presence of
- A stressful life situation that may create a conflict in relation to work
- So-called everyday aches and pain (fatigue) while performing repetitive manual work
- A strong belief in the patient that repetitive movements can damage upper limb tissues
- Confirmation of this view from colleagues, unions, politicians, the media, etc
- A medical diagnosis and certification of occupational injury, in spite of the absence of accepted physical signs of injury
- Easy access to workers' compensation
- An advantageous socio-political environment for the acceptance as a compensable disorder
Culpin reached the same conclusion about writer's cramp and telegraphist's cramp . Drawing a parallel to these conditions, Lucire stated that the patients' multimodal symptoms with elements of somatization and conversion 
, and the epidemiology and natural history of both conditions were unknown in any organic disorder . According to Lucire and Williams, the very idea that one can and has been injured creates the neurosis .
In Hunter's textbook on occupational medicine published in 1975, "occupational cramp" was still the umbrella concept covering occupational "overuse" disorders. Hunter stated that the symptoms are triggered during the execution of a customary act involving complex, rapid and repetitive movements that are developed to perfection with a high degree of precision through training and experience. The disease develops when the demands exceed a certain level. The necessary coordination breaks down, and spasm, tremor, pain, weakness and loss of control occur in muscles that are accustomed to perform harmoniously the concerned act. Still, he regarded occupational cramps as psychoneuroses due to a psychological component of tension and nervousness that is connected with an attention to getting the job done in time and with the required quality, and because symptoms could develop with normal work when physical or psychological stress impairs the performance .
Although there was almost a century since the views of Gowers  were presented, Hunter supported his theories because no structural changes were described in the nervous system or the muscles, whereas psycho-neurotic symptoms could be identified by a careful and detailed clinical interview. Hunter described the various perceptions regarding the pathophysiology as alternating from physical exhaustion of muscles and nerves to a disorder of behavior, although he recognized that the causes could be multiple and of a both physical and mental character . A diagnostic feature in Hunter's view was that the symptoms were limited to writing, and he emphasized the importance of separating writers' work-related conditions from other painful and paralytic affections and from simple pain resulting from excessive writing.
He regarded the prognosis for established disease as poor if the patient was not completely released from writing, and if there was no other external cause than writing. Treatment should be immediate to be effective. A month relief could often alleviate most symptoms, but six months could be necessary. He recommended writing with the intact hand - and a typewriter in severe cases - and suggested the administration of sedatives, massage and exercises to relieve spasms and pain .
Newer editions of Hunter's textbook have moved away from the previous interpretation and stated that three quarter of work-related upper limb disorders cannot be diagnosed according to diagnostic consensus criteria .
More recent interpretations
Based on social and moral evaluations, many experts in upper limb disorders continue to view psychological issues, including compensation issues, as the main etiologic factors in unexplained upper limb pain.
Psychosocial interpretations continued throughout the twentieth century. More recent psychiatry interpreted occupational spasm or cramp as a psychiatric condition , a conversion reaction , and as a psychosomatic illness in obsessive and dependent individuals with previous unresolved conflicts  
, but also as a form of learning or conditioning in mentally healthy subjects .
Lucire's  and Culpin's  perceptions of work-related "overuse" upper limb disorders as psychogenic since muscles cannot become dysfunctional and painful for one activity, but not for another       were supported in Brains neurological textbook in which a primary psychogenic cause was emphasized rather than a cortical fatigue condition or an organic disorder of the basal ganglia .
Awerbuch summed up the general view when the Australian epidemic of repetition strain injury peaked in the early 1980s by stating that abnormal diagnosis behavior leads to abnormal illness behavior in the patient, and that this is invariably compounded by abnormal treatment behavior .
Arguments against regarding work-related "overuse" disorders as occupational "neuroses" or psychiatric conditions
The views of Gowers , Cassirer  and Oppenheim  were opposed by Beard who rather than an occupational "neurosis" regarded writer's cramp as a primary peripheral neuromuscular disease that would rather occur in people of a strong, often very strong constitution, and is quite rare in the nervous and fragile . Paul argued that what was perceived as occupational "neuroses" was due to local damage to muscles and nerves near tendons, fascia and joints resulting from repeated impacts and tensions of short duration . Other neurologists perceive spasmodic writer's cramp as a localized dystonia  .
Merskey addressed the lack of positive criteria for diagnosing a psychiatric condition . Sheehy and Marsden regarded any psychiatric disorder in these patients as either secondary to the condition or as a random occurrence .
Macfarlane et al. argued against a single uniform etiology  because the onset of arm pain could be related to work-related psychosocial exposures in addition to mechanical exposures, but also to other aspects of health and somatic symptoms. This statement supports the dominant hypotheses in 19th century, which argued that constitutionally vulnerable neurasthenics were prone to develop neuralgic upper limb symptoms that at the time were categorized as neurotic .
Authors such as Norstrom acknowledged that a neurotic disposition or reaction manner with established disease worsened the prognosis . Oppenheim also conceded that a combination of occupational neuroses with neuritis might occur .
Occupational cervicobrachial disorder (OCD), repetition strain injury (RSI) and cumulative trauma disorder (CTD)
Occupational cervicobrachial disorder (OCD) was described in Japan as a condition with chronic fatigue and pain in the neck and upper limbs related to work tasks, which were characterized by repetitive work and possibly mental stress . A similar condition, repetition strain injury (RSI), which developed epidemically in Australia, was particularly linked to office work   . cumulative trauma disorder (CTD) was a similar construct in the USA . The RSI, which became the common covering term in Anglo Saxon literature, was not regarded as a localized syndrome but of a more diffuse character, and apparently affecting muscles. There was, however, little understanding about the etiology, pathogenesis and pathology of this condition, and why once it has occurred, it seems to continue to exist despite prolonged relief of the patient .
While these designations could be convenient for the physicians, and for the patient who now became convinced about the disease and its cause, they were less useful for treatment and prevention. Furthermore, they incorporated tautological considerations about causation but without indicating any specific mechanisms, and said nothing about the pathology. The constructs of OCD, RSI and CTD have been criticized and regarded as caused by medical and social iatrogenesis, or again viewed as somatization, hysterical, depression or other psychiatric conditions. They have also been considered as conversion of indisposition meaning that everyday common symptoms that are prevalent among all workers lead to more severe and persistent complaints in people who face difficulties in coping with their work or life due to limited personal resources. Authorities such as doctors and lawyers were alleged as responsible for supporting such a mechanism .
A muscular etiology for chronic "overuse" upper limb conditions was suggested by Ferguson, who described occupational myalgia in Australian telegraphists  and later in industrial workers  although he described neurotic personalities among the former but not the latter group of workers.
The muscle damage hypothesis for RSI got significant support  , and remains the standard for many researchers and clinicians. Several authors have discussed the similarity with primary fibromyalgia syndrome    and with reflex sympathetic dystrophy, although RSI was suggested to represent a different disease entity, with vasodilation and decreased vasomotor response characteristic for the former .
Focal dystonia represents a cluster of symptoms that associates to the descriptions of upper limb "overuse" disorder. By testing the H-reflex Nakashima et al. in 1989 could objectively demonstrate upper limb dysfunction in patients with spasmodic writer's cramp with disturbed reciprocal inhibition in the forearm flexors during writing leading to agonist and antagonist muscle co-contraction .
A vascular basis for repetitive strain injury was studied by Pritchard who demonstrated a relatively contract radial artery in patients with diffuse forearm pain compared to controls, and that the artery does not dilate with use of the limb. The diffuse forearm pain was interpreted as related to a physiologic claudication in the working forearm muscles  with pain and paresthesia occurring with muscle exertion when the intra-compartmental pressure is increased. This will cause relative ischemia of the capillary supply of the peripheral nerves in the compartment . Further elaboration on this theory has demonstrated that surgical decompression for forearm compartment can relieve pain in writer's cramp .
Contemporary researchers and clinicians  have supported the view of neurologists in the late nineteenth century that discrete upper limb peripheral nerve dysfunction were related to minor peripheral nerve lesions caused by occupational factors . The concept of adverse nervous tension  and treatment modalities based on this concept  has addressed this issue.