J Clin Pathol: first published as 10.1136/jcp.25.11.1004-c on 1 November 1972. Downloaded from 1004 The Association of Clinical Pathologists: 89th general meeting information on the origin of particular lymphocytes procedure which will avoid with particularly in relation to tumours of the lympho- certainty any of the types of , reticular system. including necrosis. It has been assumed that all types ofdecompression Functional Disorders of the Lymphoreticular System sickness are due to the formation of bubbles of H. E. M. KAY (Royal Marsden Hospital, London) during decompression and that more Functional disorders of the lymphoreticular system efficient decompression would prevent this. These may arise through primary defects of phagocytosis assumptions are being questioned and alternative of antibody formation or of T-cell function. There is theories of the pathogenesis of decompression considerable interaction between the components of sickness are being put forward, but at present no the system so that an apparent failure ofmacrophage convincing and coherent explanation of all these function may be due to lack of antibodies or of phenomena of decompression sickness has been lymphokines, eg, lack of MIF in lepromatous constructed. leprosy. Conversely, failure of macrophages to It seems probable that all decompressions are process antigen, as in the Wiskott-Aldrich syndrome, accompanied by some bubble formation, but that leads to lack of antibodies and effective lymphocyte other body changes, eg, in the blood, may be more activity against certain classes of antigen. important than has been thought hitherto. The very number of components of the system, Aseptic necrosis of bone occurs in about 20% of however, enables compensatory mechanisms to come compressed air workers and divers. In a small into play when a single activity is absent, eg, pure proportion of cases it can lead to marked disability, IgA deficiency, thymic aplasia, and the lazy leuco- particularly if the hip joints are affected. It seems cyte syndrome. At present methods are being likely that bone necrosis may arise from the opera- elaborated to identify the precise step which is at tion of several factors during the processes of com-Protected by copyright. fault in each functional disorder, as in the different pression or decompression or both, but further forms of chronic mucocutaneous candidiasis, so that observations are required on human bone tissue of appropriate therapy, eg, by transfer factor or thymic which there is a great scarcity in these cases. transplantation, can be given. Autoimmunity can arise in many ways through Observations on Haematological and Biochemical ddiciency of T-cells, or by misinformation during Parameters K. J. MARTIN (Royal Naval Physiological T-cell/B-cell collaboration. Neoplasm ofthelymphoid Laboratory, Gosport) A series of experiments system can arise from any of the components and designed to determine normal levels for selected may give rise to functional disorders such as auto- haematological and biochemical parameters in the immunity or to deficient normal function by inter- context of a simulated hyperbaric exposure devoid ference with homeostasis, eg, hypogammaglobulin- of signs or symptoms of decompression sickness. aemia in chronic lymphatic leukaemia. The parameters studied included platelets, , enzymes, plasma cortisol, and coagulation factors. The experiments were designed to differentiate http://jcp.bmj.com/ Symposium II between the true effect of and the psycho- somatic response to the situation. A control group Decompression sickness was included. The results indicate a biphasic response to the Aetiology ofDecompression Sickness R. I. MACCALLUM exposure. Immediate effects were noted with regard (Nuffield Department ofIndustrial Health, University to steroid and free fatty acids indicative of an

of Newcastle-upon-Tyne) Tunnellers, caisson wor- influence on , and changes in euglobulin on September 29, 2021 by guest. kers, and divers who are exposed to air pressure lysis activity pointed to a psychosomatic response. above normal may suffer from Delayed effects were found in the platelet, aspartate decompression sickness after the pressure is reduced aminotransferase, alkaline phosphatase, and creatine to the normal level. Acute decompression sickness phosphokinase studies. Residual effects of previous presents as pain in a limb (the bends, type I decom- diving experience were attributed to some of the pression sickness) or as a variety of signs and enzyme patterns elicited. symptoms affecting the central nervous, vascular, or It was concluded that a normal symptom-free respiratory systems (type II). Chronic sequelae are hyperbaric exposure induces a series of changes, aseptic necrosis of bone (, caisson some of which are similar to those seen in the post- disease of bone) and neurological complications. traumatic situation. It is upon this baseline that There may be other long-term defects such as damage results obtained in cases of decompression sickness to the vestibular apparatus. There is at present no are superimposed. Subclinical changes of this nature J Clin Pathol: first published as 10.1136/jcp.25.11.1004-c on 1 November 1972. Downloaded from The Association of Clinical Pathologists: 89th general meeting 1005 may produce short- or long-term effects, both in initial exposure to a hyperbaric environment and terms of adaptation and possibly even of pathology. may be seen within four months. These lesions may remain static or progress to a structural failure of the Radiology of Dysbaric Osteonecrosis J. DAVIDSON joint surface and then to secondary osteoarthritis. (Department of Radiology, Western Infirmary, In the medulla the earliest features are small areas Glasgow) Exposure to a hyperbaric environment of increased density and small foci of calcification either in tunnel work or diving may result in the which eventually become quite large. Any attempt to acute type I or type II forms of decompression reduce the incidence of the condition must be moni- sickness ('the bends') and also the late complication tored by high quality radiology and there must be a of aseptic necrosis of bone-sometimes called high index of suspicion in those areas at risk. In a caisson disease of bone, barotraumatic osteoarthro- few cases we have been able to correlate the radio- pathy, etc. Dysbaric osteonecrosis is now the accepted graphic and pathological findings and this has been term and includes the rare forms of osteonecrosis of immense value in identifying the earliest features following exposure to a low pressure environment. with confidence. Many report thickening of the Dysbaric osteonecrosis is a major to trabeculae or small as the earliest evidence of compressed air workers and an increasing danger to osteonecrosis but these radiographic findings have divers especially with longer exposure times at not been substantiated at histopathology. For this greater depths. Young men, often in their 20s, may reason and because these changes can be identified develop a painful of the shoulder or hip in those not at risk we have not recorded these joint with consequent permanent disability. findings as positive. Clearly then there is much scope While the condition has been known for many years for further correlation between pathology and the diagnosis was rarely made until the bone changes radiology. This would be of immense value. were sufficiently advanced with an associated The diagnosis of dysbaric osteonecrosis is not structural failure of the articular surface causing usually difficult and all other causes of aseptic Protected by copyright. symptoms. The first attempt to identify the incidence necrosis of bone must be kept in mind. The most of dysbaric osteonecrosis was carried out in Glasgow important ones to be excluded are those following in 1963 when the entire labour of 250 men fracture of the femoral neck or dislocation of the constructing the Clyde tunnel were examined radio- hip, the idiopathic form sometimes associated with graphically andthefindingsrelatedtotheoccupational large doses of steroids, the haemoglobinopathies, history. The incidence of osteonecrosis was 19 % Gaucher's disease, and Schandler's disease. and in 10% of the men the lesions were juxta-arti- Necropsy radiographs of the chest following cular and, therefore, potentially disabling. Since then diving fatalities have been of considerable interest, all compressed air workers in the United Kingdom demonstrating widespread intravascular gas/air in have had a radiographic skeletal survey and the the axillary and carotid vessels. Some have shown MRC Decompression Sickness Registryhasexamined either a pneumothorax or bulla formation which 1694 men showing an incidence of 19 7 % with supports the theory that pulmonary air trapping

definite osteonecrosis and 11% with a juxtaarti- could be a cause of massive air . Two such http://jcp.bmj.com/ cular lesion. cases will be included in the paper. The head of the humerus is most frequently involved and 36 % ofthe lesions are bilateral. The next NECROPSY OF DIVING AND most common site is the distal shaft of the femur. COMPRESSED AIR FATALITIES Other sites included the head of the femur, proximal A necropsy chest radiograph can be of considerable shaft ofthe tibia, and less commonly the talus, fibula, value. It may show evidence of a pneumothorax, or humerus. The lesions have been classified into cyst or bulla formation, mediastinal emphysema. two broad groups: juxtaarticular which are next to Careful inspection of the axilla may show extensive on September 29, 2021 by guest. the surface and liable to cause structural failure with gas/air in the axillary vessels. Surgical emphysema symptoms, and medullary where the lesion is at may be present. Similarly a radiograph of both some distance from the joint surface and will never groins may show widespread gas/air in the ilio- give rise to symptoms. Further subclassifications femoral artery and vein segments. have been made according to the radiographic Antero-posterior radiographs of the head of each appearances. humerus should be coned to show optimum trab- The earliest radiographic features are areas of ecular detail and the body rotated slightly in order increased density adjacent to the articular surface that the central x-ray beam passes vertically through and these result from new bone laid on dead trab- the shoulder joint. eculae resulting in an overall increase in bone bulk. Antero-posterior radiographs of the head of each These develop about eight months to a year after femur should be coned to show trabecular detail.