The objective of this investigation was to clarify the epidemiology of idiopathic Parkinson's disease (PD) in the county of Rogaland, Norway. Total case ascertainment and a high diagnostic accuracy were attempted through a detailed community study and the use of a new clinical diagnostic classification. The study population comprised 220,858 inhabitants, and a total of nearly 400 patients was interviewed and examined by a neurologist. On prevalence day, January 1, 1993, 245 patients were included in the study. The diagnostic classification revealed 135 patients with clinically definite, 74 with probable, and 36 with possible PD. The crude prevalence rate was shown to be 110.9 per 100,000 inhabitants. The total age-adjusted prevalence was calculated to be 102.4 per 100,000 and to 120.9 per 100,000 men and 89.8 per 100,000 women. Among the 245 patients, 28 patients had a tremor-dominant disease, 50 patients an akinetic-dominant disease, and 167 patients a mixed clinical pattern of PD. Age-adjusted prevalence figures were slightly higher for rural compared to urban areas. About 50% of the PD patients were in need of public help, 15% had complaints about pain related to their parkinsonism, and after approximately 6 years of levodopa treatment, 20% were suffering from clinical fluctuations. The study showed that 40% of the patients had some degree of thought disorder. The prevalence figures for PD in this study are slightly lower than those reported from most previous prevalence studies with a comparable study design for case finding. This may be due to a careful diagnostic evaluation with the use of specified diagnostic criteria, excluding patients with other parkinsonian syndromes.

Myasthenia gravis (MG) is caused by autoantibodies to the acetylcholine receptor (AChR), but several other muscle autoantibodies have also been identified in patient sera. We studied muscle autoantibodies against AChR, striated muscle tissue sections (SH), titin, citric acid antigen (CA), and ryanodine receptor (RyR) in sera from 146 consecutive MG patients to evaluate whether a single test or several tests together can predict a thymoma. The MG patients were divided into five subgroups; ocular MG, early-onset MG (< 50 years), late-onset MG (> 50 years), MG with thymoma, and AChR antibody negative MG. AChR, SH, titin, CA, and RyR antibodies were detected in 85%, 34%, 34%, 25%, and 14% of the MG patients, respectively. For thymoma MG, AChR, SH, titin, CA, and RyR antibodies were detected in 100%, 75%, 95%, 70%, and 70% respectively. SH, titin, CA, RyR antibodies, and computed tomography of the anterior mediastinum have similar sensitivity for thymoma MG. The specificity of RyR, titin, CA, and SH antibodies for thymoma was 70%, 39%, 38%, and 31%, respectively, which is significantly higher for RyR antibodies than for the others. No single muscle antibody assay can predict a thymoma, and a combination of several antibody assays is preferred, although RyR antibody testing alone showed 70% sensitivity and specificity for thymoma MG. SH and CA antibodies provided only little additional information.

We have defined myasthenia gravis (MG) in the elderly as onset after the age of 50 years. MG is diagnosed more often today than previously. The increase is mainly found in patients over the age of 50 years. Neurologists therefore see more old patients with MG now than before. Prevalence of the early-onset form of MG seems to be unchanged. Recent data indicate that MG may still be substantially underdiagnosed in very old people. Ptosis, diplopia, weakness of the facial muscles, and problems of articulation are important clinical signs in MG and are easier to detect in a youthful appearance. Since ageing causes a decrease in the total eyelid area with sagging of the lower eyelids, a ptosis may be more difficult to diagnose in the elderly. In addition, diplopia may not be detected because of reduced vision due to macular degeneration or cataract formation. Ocular symptoms of MG are therefore more easily missed in the elderly. Thymomatous MG is more common among older patients than it is in younger onset. The mean age at onset of MG for thymoma cases is 50-60 years. Approximately 10-15% of all MG patients have a thymoma, and around 40% of all thymoma cases are associated with MG. During normal aging, the thymus tissue becomes atrophic and replaced with fat. Recent data on MG thymus pathology suggest that lymphocyte accumulation indicating residual thymus may also be found in the elderly, and that there is little qualitative difference between the young and the old thymus from MG patients. The mean concentration of antibodies to acetylcholine receptor (AChR) is lower in MG in the elderly than in early-onset or thymoma-associated MG. Seronegative MG is less common among older patients. Approximately 30% of patients with late-onset, nonthymoma MG have antibodies to titin, while such antibodies are extremely scarce in early-onset MG. Titin antibodies in MG patients seem to be associated with a higher frequency of DR7 antigen and a decrease of DR3 antigen. The antibody response in MG may therefore be influenced by the genetic background.

Approximately 15% of patients with myasthenia gravis (MG) have thymus neoplasia. These MG with thymoma (MGT) patients show autoantibodies to striated muscle as well as autoantibodies to acetylcholine receptor. To characterize these thymoma-associated muscle antigens, we cloned a number of immunopositive cDNAs by immunoscreening muscle cDNA libraries with sera from MGT patients. Analysis of the isolated cDNAs show that all share a common sequence encoding a distinct region of the titin gene. We expressed this main immunogenic region (MIR) of titin in Escherichia coli, and determined autoantibody serum titers directed against the obtained recombinant antigen in a variety of patients. We could detect titin MIR autoantibodies in 97% of sera from MGT patients but not in control sera from healthy blood donors. Therefore, expressed titin from the MIR of the molecule is a sensitive marker antigen for evaluating the presence of thymoma in MG.

Non-AChR muscle autoantibodies occurred more frequently in severe MG regardless of MG subgroup. Thymoma per se does not generate a more severe MG. It may well be the presence of a humoral immune response to non-AChR muscle antigens such as titin, citric acid antigen, and ryanodine receptor that leads to a severe disease, not the presence of thymoma or a late age of onset. These antibodies can serve as important prognostic markers in MG regardless of the presence of thymoma.