Klinische Wochenschrift

Klin Wochenschr (1983) 61:509-515

Springer-Verlag 1983

Myasthenia Gravis: Overlap with 'Polyendocrine' Autoimmunity W.A. Scherbaum i . , F. Schumm 2, B. Maisch 3, Claudia M/iller 3, A. Fateh-Moghadam 5, S.H. Flfichter 4, F.J. Self ~, G.F. Bottazzo 6 and P.A. Berg 3 1 Medizinische Poliklinik, 2 Neurologische Klinik, 3 Medizinische Klinik, and 4 Department of Urology, Chirurgische Klinik, University of Tiibingen, s Institute of Clinical Chemistry Grosshadern, University of Munich, Department of Immunology.. Middlesex Hospital Medical School, London 6

Summary. 81 patients with spontaneously acquired myasthenia gravis (MG) were investigated for the presence of autoimmune (AI) diseases and their sera were tested for a range of organ-specific autoantibodies. 77 of the patients were HLA-phenotyped. Antibody titres to acetylcholine receptors (AChR) were higher in non-thymomatous patients who possessed HLA-B8 (p<0.05) and/or -DR3 (p<0.05) as compared to patients lacking these HLA antigens. 3 out of 20 (15%) patients with ocular MG, 7/23 (30%) with generalized MG of early onset, 11/23 (48%) generalized MG of late onset and 5/14 (35%) patients with thymoma had either overt AI diseases or significant titres of organ-specific autoantibodies suggesting subclinical AI disease. In ocular MG, low titres and an infrequent finding of antibodies to AChR (32%) as well as the low prevalence of associated autoantibodies and A1 diseases indicate that this subgroup of MG consists of patients with restricted AI reactivity. HLA-B8 a n d - D R 3 were present in all the patients with associated AI disorders in the young onset group but in none of the patients with old age of onset. In the young group, 6 out of 7 patients with associated AI conditions were women whereas the sex ratio was about equal in the older cases in both, patients with and without associated AI diseases or autoantibodies. We conclude from these observations that ageing provides conditions that allow the breakdown of self tolerance. The simultaneous presence of HLA B8, DR3 and * This work was finalized when W.A. Scherbaum was a research associate at the Department of Immunology, Middlesex Hospital Medical School, London, U . K . W . A . Scherbaum is supported by the Deutsche Forschungsgemeinschaft Sche 225/i-2 Offprint requests to: Dr. W.A. Scherbaum (address see page

515)

female sex provide important additional factors for early expression of MG.

Key words: Myastenia gravis - Autoimmune diseases - Autoantibodies - HLA

Introduction Autoimmune (AI) mechanisms play a major role in the pathogenesis of spontaneous acquired myasthenia gravis (MG) which may present either in a generalized form or be confined to ocular muscles. The disease consists of heterogeneous subgroups as indicated by differences in clinical features, sex, age of onset [52], thymus pathology [9] anti-acetylcholine receptor (AChR) antibody titres [61], and response to specific therapy [51]. The importance of genetic factors for the development of MG is indicated by HLA studies [20, 11] and the frequent observation of associated AI diseases [39, 14, 17, 26] and autoantibodies [20] in myasthenic patients and their close relatives [8]. No attempts have been made so far to find out whether patients with associated AI reactions to other organs represent a special subgroup of MG. A number of AI diseases have been described in patients with MG [7, 24, 26, 28, 31, 33, 34, 39, 44, 54, 59]. Most of them rely on single case reports which cannot provide a true picture of the association of MG with other AI diseases in general. The major aim of this study was to establish the clinical and subclinical autoimmune diseases associated in a series of patients with MG and to characterize the HLA phenotype of such patients in comparison to that of other MG patients. In this paper we will focus on organ-specific AI diseases and autoantibodies.

5]0

W.A. Scherbaum et al.: Myasthenia Gravis and 'Polyendocrine' Autoimmunity

Table 1. Mean age, age of onset and sex ratio in 81 patients with different types of spontaneously acquired myasthenia gravis (MG) No thymoma

Mean age Age of onset [cases]

Total studied Males Females Sex ratio M/F

Thymoma

ocular MG

generalized MG

49 (29-76) 47 (22-76) [20]

44.7 (16-82) 38.9 (2-75) [46]

20 16 4 4:1

onset <40

onset >40

23 5 18 1:3.6

23 10 ]3 1:1.3

50 (28-67) 42 (28-62) [7]

15 7 8 1:1.1

Patients Sera of 81 unrelated caucasian patients with acquired MG were examined in Southern Germany. The diagnosis was proven by neurological and electrophysiological investigation including a Tensilon test. A summary of the type of MG, mean age of the patients at the time of clinical investigation, age at onset and sex ratio is given in Table 1. Drug-induced cases [48, 49] were excluded. In some cases, MG was inactive at time of serum investigation. 38 patients had been thymectomized and histological examination showed a thymoma in 13, thymus hyperplasia in 23 and persistent thymus in 2 cases. 2 thymoma cases had not been operated because of severe cardiac disease in the presence of only mild myasthenic symptoms. All patients were examined neurologically by one of us (F. Sch.) and most of them underwent endocrinological and cardiological examination by another (W.A. Sch.). HLA-antigens were determined in 74 patients and AChR-Ab were measured in all of them.

Methods

Antibody Tests: The indirect immunofluorescence (IFL) test was employed to detect antibodies to various tissues using unfixed 4 gm cryostat sections. The sera were tested undiluted for organ-specific, and 1 : 10 for non-organ-specific and muscle antibodies and those positive were titrated at doubling dilutions to endpoint. FITC-labelled conjugate of anti-human gammaglobulin was purchased from Wellcome Reagents Ltd. As substrates we used human pancreas, adrenal gland, ovary, testis, placenta and skeletal muscle of donors with blood group 0, human kidney of donors with blood group A, and rat stomach, rat heart muscle, rat skeletal muscle. Heterophil antibodies were excluded in all the sera tested. Sera positive for gastric parietal cell antibodies at titre >1:10 were tested for antibodies to intrinsic factor by a radioimmunoassay. Thyroid microsomal (MCHA) and thyroglobulin antibodies (TGHA) were determined using the passive haemagglutination technique [23, 66] and commercially available test kits (Fujizoki, Japan) with a basal dilution of patients' sera ] : 100. MCHA titres of > 1:6,400 and/or TGItA titres of > 1:400 were considered as signs of autoimmune thyroiditis. Antibodies to pancreatic islet cells and to adrenal cortex were considered significant when detectable in undiluted serum. Antibodies to the acetylcholbw receptors (AChR-Ab) were determined using a sensitive radioimmunoassay based on the

immunoprecipitation of tz5I-alpha-Bungarotoxin(Bgt)-labelled acetylcholine receptors [32]. Human muscle membranes were extracted in Triton X-100, and the solubilized proteins were exposed to a saturating concentration of lZSl-alpha-Bgt. The complexes of IgG and AChR formed over a period of 4 hours were precipitated by addition of goat anti-human IgG serum. The presence of AChR in the precipitate was determined by counting ~zSI-alpha-Bgt bound to it. The results were expressed in nmoles of alpha-Bgt binding sites precipitated/1 serum. Antibody titres of 0.4 x ]0 -9 and greater were regarded as elevated [58]. HLA-testing. The HLA-ABC antigens of patients and controls were determined in the standardized microtoxicity assay [56]. HLA-DR typing was performed on nylon-wool separated B-lymphocytes [35] in a microcytotoxicity assay with prolonged incubation times [4]. Only antisera of the 8th International Histocompatibility Workshop 1979 (disease-set) as well as locally well-defined antisera were used to define the HLA-A, -B, -C, and -DR antigens. Thyroid function tests were performed in all patients with a goitre and/or thyroid antibodies. They included determination of serum thyroxine, triiodothyronin, and serum-TSH. The TRH-test was performed measuring circulating TSH levels before, and 20 rain after injecting 400 Ixg TRH iv (normal increase: >2.5-fold, peak TSH <20 mU/1). Goitrous autoimmune thyroiditis was diagnosed when a goitre and MCHA > i : 6,400 and/or TgHA > 1 : 400 were present [47]. Cytological or histological verification of the diagnosis was not attempted. Euthyroid goitres without thyroid antibodies or a history of thyrotoxicosis will not be discussed here since they are mostly due to iodine deficiency in the endemic area of Southern Germany [27]. Significance values were calculated using the 2"2 test to compare antibody titres, and Fisher's exact test with Yates' correction for comparison of associations.

Results

Antibodies to acetylcholine receptors ( A C h R - A b ) w e r e p o s i t i v e in 6 o u t o f 6 ( 1 0 0 % ) t h y m o m a c a s e s t e s t e d , in 6/19 ( 3 2 % ) n o n - t h y m o m a t o u s p a t i e n t s w i t h o c u l a r M G , a n d in 33/43 ( 7 7 % ) n o n - t h y m o matous patients with generalized MG. All patients with thymoma tested showed titres higher than 12 x 10 - 9 nmol/1. M e a n t i t r e s o f A C h R - A b w e r e l o w e s t i n o c u l a r M G (1.6_+3.5 n m o l x 1 0 - 9 ) , h i g h er in t h y m o m a p a t i e n t s (46 + 56.1), a n d h i g h e s t in n o n t h y m o m a t o u s f e m a l e s w i t h a g e o f o n s e t < 40 (62.2_+ 127.5). T h e t i t r e s o f A C h R - A b w e r e h i g h e r in p a t i e n t s w i t h n o n - t h y m o m a t o u s M G w h o p o s s e s s e d H L A - B 8 (p < 0.05) a n d / o r - D R 3 (p < 0.05) as c o m p a r e d t o p a t i e n t s l a c k i n g t h e s e a n t i g e n s . Antibodies to striated muscle fibrils ( A F A ) w e r e p o s i t i v e i n 13 o u t o f 14 ( 9 1 % ) p a t i e n t s w i t h a t h y m o m a , in 5/20 ( 2 5 % ) o f c a s e s w i t h o c u l a r M G , 1/23 ( 4 . 3 % ) w i t h g e n e r a l i z e d M G o f y o u n g o n s e t a n d 10/23 ( 4 3 . 4 % ) p a t i e n t s w i t h o n s e t a t o l d age. A F A w e r e m o r e c o m m o n in m a l e s (16 o u t o f 48) t h a n in f e m a l e s (12/72), ( p < 0 . 0 5 ) , a n d t h e y w e r e m o r e f r e q u e n t i n p a t i e n t s o v e r 50 (15/30) as c o m p a r e d w i t h y o u n g e r p a t i e n t s (2/36).

W.A. Scherbaumet al.: MyastheniaGravis and 'Polyendocrine' Autoimmunity

Associated

ocul.ar Me

~eneralized MG

autoimmune condition

onset <40

onset >40

.oitrous AIT Primary

511

?

myxoedema

~raves" thyrotoxicosis Idiopathic Addison's Pernicious anaemia + goitrous AIT

O~

Type I

~

diabetes

Vitiligo

0~

Islet-cell antibodies

O~

Adrenal antibodies Thyroid

~

O~

~ ~

McHA >1:1600 TEHA >I:400

auto,mmune co.dition

O"O"O"O"C ? O~O~O~0 ~

~~

~

~

o~o~ ? ? 0~

Fig. 1. Associated overt and subclinical a u t o i m m u n e diseases in n o n - t h y m o m a t o u s patients with spontaneously acquired ocular (n = 20) a n d generalized (n = 47) myastenia gravis. ~ = male, ~ = female. • = H L A - B 8 and D R 3 positive. ¢ = only H L A - D R 3 positive. = only H L A - B 8 positive. ~ = H L A - B 8 and -DR3 negative, o = H L A n o t tested. A I T = a u t o i m m u n e thyroiditis

Associated Organ-specific Autoimmune (AI), Diseases in Patients with Different Forms of Myasthenia Gravis (MG) The sex distribution and the mean age of patients in each form of M G are given in Table 3.

1. Ocular MG Three (15%) of these patients had some evidence of AI disease (Figure). Two (10.5%) out of 19 showed an H L A A1-B8-DR3-positive phenotype. One of the two was a Hashimoto case and the other had parietal cell antibodies (titre 1:20). 3 were only positive for either DR3 or B8, and 13 had none of these H L A antigens (Figure i).

2. Non-thymomatous Generalized MG of Young Onset (< Age 40) Seven (30.4%) of 23 individuals had associated AI diseases with their corresponding antibodies (n = 4) or significant titres of autoantibodies without overt

AI disease (n = 3). 6 of the 7 were females. 13 (59%) of 22 patients tested for H L A antigens expressed both, B8 and DR3 (Fig. 1). 3 out of 8 patients with an H L A A1-B8-DR3-positive phenotype and 4 out of 5 with a BS-DR3-positive phenotype had associated AI conditions. All the 7 patients with associated AI conditions possessed both, the H L A B8 and DR3 antigen. 6 of the 7 had been thymectomized and the histology showed thymitis in each case.

3. Non-thymomatous Generalized MG with Onset at Old Age ( > 40) Thirteen (56.5%) of 23 patients in this group had associated organ-specific AI diseases (n = 8) or significant titres of autoantibodies (n = 5). 2 additional cases had low titres of parietal cell antibodies and were negative for intrinsic factor antibodies. Only one out of 17 individuals was typed H L A B8, DR3 positive, 6 patients expressed either B8 or DR3 and 10 patients were negative for these H L A antigens (Figure 1).

512

W.A. Scherbaum et al.: Myasthenia Gravis and 'Polyendoc~ine' Autoimmunity

T a b l e 2. HLA types in different forms of non-thymomatous myastenia gravis. The p-values express the significance of differences between two groups and the arrows point to the group with an increased prevalence o f an H L A phenotype. NS = not significant

H L A type

Ocular M G

Generalized M G onset < 40

A1 +

4

11

5

NS A1-

15

A3 +

8

onset > 40

NS 11 4

10 p <0.03

--*

A3-

11

18

7

B7+

5

3

7

B7-

14

B8+

3

NS

B8-

16

DR2 +

10

NS 19

10

14 ~

3 ~

p<0.02

8

14

8

11

NS DR2-

9

DR3+

5

DR3 -

NS 14

B8+/DR3+

2

-~

1 ~-

p<0.02

9

10

13 p<0.005

B8-/or DR3--

12

13 p<0.02

12

NS 9

2

BS-/DR3-

5

~

14

B8+/DR3+

6

13 p < 0.07

17

~

1 ,-

p<0.003

9

16

Table 3. Significance values for HLA B8 when non-thymomatous females and males with generalized myastenia gravis of different age of onset are regarded separately. H L A B8 is more common in females of young age at onset as compared with females and males with old age of onset. N S = n o t significant, F = females, M = males

H L A B8 +

Onset < 40

Onset > 40

males

females

females

2

15

HLA B8-

4

males

2 NS . . . .

•

F+M 6

2 •

7

F+M 9

p < 0.02 • (

............

F 0'-

F

Five (35%) of the 14 patients with thymoma had conditions with an autoimmune background: Graves' thyrotoxicosis with thyroid and adrenal antibodies (1), vitiligo (1), myositis (1). One had adrenal plus thyroid antibodies and I had high titres of thyroid antibodies in the absence of the corresponding disease. One additional patient had parietal cell antibodies (titre 1:40) but no antibodies to instrinsic factor.

12

NS

p<0.0003

4. MG with Thymoma

•

F p < 0.002

•

F+M

Discussion

Autoimmune (AI) diseases tend to be aggregated in families and the concept of 'polyendocrine autoimmunity' [13] points to the involvement of several (endocrine) organs in one individuum. Acquired myasthenia gravis (MG) is an organ-specific AI receptor disease and its overlap with AI endocrine diseases [4, 17, 26, 39] and autoantibodies [20] suggests common etiologic factors. The presence of associated autoantibodies in the serum of 74 MG patients analyzed may point to an underlying tendency to AI reactivity [45]. AI diseases such as Type I diabetes and AI Addison's disease only represent more severe cases, the expression of which depends on additional triggering factors [5, 46]. The association of MG with thyroid A1 diseases is well shown by many case reports of Graves' thyrotoxicosis and Hashimoto's thyroiditis [2, 3, 6, 12, 16, 40, 43, 50, 53, 54, 65]. The inclusion of sensitive thyroid function tests and antibody determination now allows to recognize AI thyroiditis even without overt disease [47]. However, goitres are so common in the iodine dificient area of Southern Germany [27] that in the absence of histological proof of Hashimoto's disease, the constellation of a goitre and significant titres of thyroid antibodies is here classified as 'goitrous autoimmune thyroiditis'. Differences in clinical features [15], thymus pathology [9], immunological findings [55], and HLA associations [20, 11] suggest the separation into at least four subtypes of spontaneously acquired MG [38]. Non-thymomatous ocular MG, generalized MG starting below 40 years, generalized MG in older subjects, and cases with thymoma. Dividing the patients into these groups has enabled to show significant correlations with certain HLA types which could not have been made when the patients were considered as a whole [62]. The question is whether some of these four

W.A. Scherbaum et al.: Myasthenia Gravis and 'Polyendocrine' Autoimmunity

groups are at higher risk to develop other AI diseases or whether AI reactivity occurs randomly in myasthenic patients. Patients with ocular M G may be separated from those with generalized disease because of their male preponderance, their poor response to anticholinesterase drugs and improvement through steroid treatment [18, 21]. Investigating sera from myasthenic patients Garlepp et al. [25] found an increase of thyroid antibodies in patients with restricted ocular MG. However, these studies were performed on sera of patients from several different races and clinical details were only provided by questionaires. Our data on an ethnically u n i form group of endocrinogically investigated patients show that associated AI disorders are rare in patients with ocular M G who seem to have restricted AI features. This view is supported by the low prevalence and titres of AChR-Ab which in these cases tend to react stronger with eye muscle antigens [60] and A C h R derived from denervated peripheral muscles [64]. 30% of patients with early onset of generalized M G had associated clinical or subclinical AI diseases. Similar figures were found in the series of Feltkamp et al. [20], Oosterhuis [39] and NewsomDavis' group [11]. It is of interest that all our 'autoimmune' patients in this group possessed HLAB8 and -DR3 antigens whereas in patients without associated AI diseases, HLA-B8 and-DR3 were present in only 40%, and the prevalence of this haplotype in the normal population is 0.1%. AChR-Ab were significantly higher in females than in males with generalized M G of early onset. Like Naeim [36], we found that AChR-Ab titres were higher in patients who possessed H L A B8 and -DR3. These data support the suggestion of Compston et al. [11] that females with these antigens represent a separate group of patients who are both, more susceptible to M G and who are better antibody producers than others in the same age group. Unlike Addison's disease [57], Graves' thyrotoxicosis [19], and Type I diabetes [10], the association with HLA-B8 in myasthenic patients is stronger than the one with H L A DR3. This has also been noticed by others [29, 41, 42] and it has been argued that there might be substancial genetic differences between M G and the above mentioned AI diseases. However, this statement does not hold true when the different groups of M G are analyzed separately (Table 1). Virtually all the patients with generalized M G of early onset who were positive for H L A B8 were also positive for DR3 and in our patients the constellations D R 3 + / B 8 or

513

B8 + / D R 3 - only occurred in ocular M G and in the late onset group of generalized M G both of which do not show an increased prevalence of these H L A antigens. H L A B8 does not exceed the prevalence of DR3 in our early onset group of M G which shows an increase of these antigens. In this series, as many as 48% of the patients with old age of onset had associated clinical or subclinical AI diseases as compared to only 30% in the young age group. This fact was also recognized by others [11] and is only poorly understood. Similar to the findings of Fritze et al. [22], there was a slight increase of H L A A3 in this group with M G of late onset. However, in contrast to the results of Compston et al. [11], an increase of B7 could not be demonstrated in our series indicating that H L A associations are weak in t]he late onset group and they may differ from one study to another. The thymus is a central immunological organ responsible for the maturation of T-lymphocytes. Similar to other studies [9], thymus hyperplasia (' thymitis') was noted in all our patients with generalized M G of young onset and these patients are also known to benefit from thymectomy [5•]. A C h R have been found on myoid cells cultured from thymuses [30] and there is now substantial experimental evidence that the thymus is the site of factors which enhance the synthesis of A C h R antibodies. These may be helper T cells since irradiated thymic cells, which are not capable of antibody synthesis increase the production of A C h R antibodies by autologous peripheral blood lymphocytes in co-culture [37]. Thymic hyperplasia is also found in the classical organ-specific autoimmune diseases such as Graves' as described by Von Basedow [i] but the anatomical position of antigen (AChR)-presenting cells within an immunological organ may explain the central role of the thymus in generalized M G [64]. However, this only applies to females with young age of onset who regularly show thymitis. In the late onset group an age-dependent breakdown of self-tolerance might be the initiating mechanism for both, M G and its associated autoimmune diseases. It is evident from our data that 'polyendocrine M G ' is not a separate entity of M G but it is rather an expression of underlying basic defects of the immune system.

Acknowledgements, We are grateful to Professor Deborah Doniach for helpful suggestions and advise. Professor H. Bockhorn from the Department of Surgery, Tfibingen University, kindly supplied fresh operative specimens. We thank Professor M. Eggstein and Professor J. Dichgans for their continuous support.

514

W.A. Scherbaum et al.: Myasthenia Gravis and 'Polyendocrine' Autoimmunity

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