Chronic idiopathic urticaria (CIU) is characterised by transient cutaneous wheals occurring daily or almost daily for more than six weeks. The pathogenic mechanism of more than 65% of patients with CIU remains unknown.1 In these patients mast cell dysfunction or local activating factors should be taken into account.2 The coexistence of CIU with autoimmunity is relatively well proven.3 This phenomenon has mainly been connected with thyroid abnormality although other associations have also been reported. Myasthenia gravis is defined as an organ specific, autoantibody mediated and T-cell dependent human autoimmune disease.4 In myasthenia patients, despite characteristic clinical features, there are numerous immunological abnormalities described, such as activation of T and B lymphocytes and epithelial cells. One of the characteristic features is anti-acetylcholine receptor antibodies production as well as the ability of cultured thymic lymphocytes to proliferate in the presence of acetylcholine receptors (AChRs).5 It is still a matter of debate whether AChR-like molecules can be expressed on the surface of other cells and trigger autosensitisation reactions or autosensitisation of lymphocytes is the primary process which takes place initially in the thymus.
Despite the variety of diagnostic procedures, the aetiology of many chronic urticaria cases remains unknown and the reason for further investigation is to find the potential comorbidities which may influence the course of urticaria. In the present study we describe two cases of chronic urticaria and myasthenia coexistence.
Case 1A 67-year-old man came under our observation reporting recurrent severe episodes of generalised urticaria and tongue angio-oedema for five years. Skin changes were localised mainly on his feet, hands and face, less often on the trunk and appeared spontaneously or/and a few hours after pressure – the diagnosis of delayed pressure urticaria was established according to current guidelines.6 Three years earlier the diagnosis of type 2 diabetes had been established and treatment with gliclazide was initiated. Five years before the present hospitalisation the diagnosis of myasthenia gravis had been established (untreated and asymptomatic during our observation). Basic laboratory findings were not specific with negative antinuclear antibodies (ANA). Anti-SM, anti-Jo1, anti-dsDNA (double-stranded-DNA) and anti-Scl-70 were negative as well. Complement parameters were normal.
Case 2A 54-year-old woman was admitted to the hospital because of recurrent severe angio-oedema and urticaria requiring numerous unscheduled medical interventions. She also reported symptoms of delayed pressure urticaria. The symptoms occurred six months before hospitalisation. The patient suffered from arterial hypertension, and underwent twice (three years before) myocardial infarction and coronary angioplasty. Four years before the present hospitalisation the diagnosis of myasthenia had been established and the patient had undergone thymectomy. Myasthenia was effectively treated with mestinon. No significant abnormalities were found in routine laboratory parameters. Serum levels of IgG, IgM and IgA were normal, and complement parameters were unremarkable. ANA, ANCA, anti-SM, anti-Jo1, anti-dsDNA and anti-Scl-70 were negative.
Autoimmunity in CIU with no doubt plays an important role. It has been suggested that 30–40% cases of CIU have in fact an autoimmune background.3 The autoimmune reactions in chronic thyroiditis and their potential role as a trigger factor in CIU have already been widely discussed and described.7 The relationship between CIU and autoimmune diseases may suggest that the myasthenia of our patients was not merely a coincidence but there is a pathological link between these two diseases. Both described cases of severe urticaria were preceded by myasthenia which is closely connected with excessive autoantibodies production. In about 80% of myasthenia gravis cases the disease is mediated by antibodies against the nicotinic AChR. These antibodies decrease the number of functional AChRs at the muscle fibre endplate by increasing their degradation and turnover. Additionally, they induce complement-mediated damage to muscle fibres, and block acetylcholine binding to the receptor. In Kageyama-Yahara et al.8 study nicotinic AChRs were proved to be expressed on mast cells presenting inhibitory effect on mast cell degranulation. As a result, nicotinic AChRs are involved in the negative regulation of mast cell activation with an anti-inflammatory effect.8 Interestingly, agonists of nicotinic AChRs were supposed to have a therapeutic effect on a murine model of food allergy.9 The above-mentioned mechanism is particularly interesting in the light of symptoms of delayed pressure urticaria in both subjects described in our study.
There are only a few reports on the coincidence of chronic urticaria and myasthenia gravis – all in distant studies. One of the reports comes from 197710 and concerned urticaria found in a patient with myasthenia and SLE. There were suggestions that myasthenia may antedate SLE, because thymus histology in SLE patients shows germinal centres similar to those seen in myasthenia. However, no benefits after thymectomy were shown in SLE cases unlike in myasthenia patients.10
To the best of our knowledge in the current literature there are no descriptions of chronic urticaria associated with myasthenia. In our opinion the coexistence of chronic urticaria and myasthenia should be more deeply explored, particularly in the light of the possible role of AChRs in mast cell activation.
Ethical disclosuresConfidentiality of dataThe authors declare that no patient data appear in this article.
Right to privacy and informed consentThe authors declare that no patient data appear in this article.
Protection of human subjects and animals in researchThe authors declare that no experiments were performed on humans or animals for this investigation.
Conflict of interestThe authors have no conflict of interest to declare
