Hydatid false positive serological test results in malignancy.

1197 The mechanism for the air in the mediastinum is suggested as being due to rupture of marginal pulmonary alveoli, allowing the development of pulmonary interstitial emphysema. This then tracks through the fascial planes at the lung hilum, and from there into the mediasti-num and neck. There was no obvious underlying lung disease in our patient, and no further investigations were indicated. His lympho-cytosis may have been secondary to a coryzal illness from which he was recovering at the time; upper respiratory tract infections have been associated with this condition.4 The relatively benign course and rapid recovery shown by the patient was in keeping with the findings of others,5 and recurrence is very unusual.4 We thank Dr G Terry for permission to report this case. 2 Macklin MT, Macklin CC. Malignant interstitial emphysema of the lungs and mediastinum as an important occult complication in many respiratory disease and other conditions: an interpretation of the clinical literature in the light of laboratory experiment.peritoneum: is it a rare cause of chest pain ? Despite advances in radiology, ultrasound, and computed tomographic imaging techniques, diagnosis of hydatid disease still relies on serological tests to distinguish between a hydatid cyst and other, similar space occupying lesions. Serological tests, however, vary considerably in both sensitivity and specificity. This variability is multifactorial, dependent on the qualitative and quantitative differences in the test antigen used, the criterion (titre) for positivity, the location and viability of the cysts, and possibly the strain of the parasite concerned. Reports of serological tests for hydatid giving false positive results in various malignant diseases appear regularly, suggesting antigenic similarity between Echinococcus granulosus and neoplasms'; a similar phenomenon occurs between bacteria and certain tumour cells. Kagan attributed these false positive reactions to autoantibodies which react with human host protein components found in hydatid fluid antigen.2 Norris was more specific3: she attributed false positive complement fixation test reactions in patients with cancer to interaction of blood group P substance in hydatid fluid4 with anti-PI antibody in sensitised patients. Norris raised the question whether neoplasms are associated with an increased susceptibility to sensitisation by the P substance in hydatid cyst fluid used as test antigen in the Casoni skin test: the patients who developed the anti-P1 antibody after Casoni tests all had carcinoma. We have used the indirect haemagglutination test and counter-immunoelectrophoresis to assess the frequency and nature of hydatid false positive reactions in patients …