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Myasthenia gravis associated with lupus nephritis

Sir – Coexistence of systemic lupus erythematosus (SLE) and myasthenia gravis (MG) may be sporadically encountered,1–4 but the immunopathogenetic basis for the association of these two clinically distinct autoimmune disorders is still unknown. Sthoeger, et al.5 have reported a high prevalence rate of SLE and lupus-related autoantibodies in patients with MG, especially in female, early onset (<40 years) and generalised type. Thymectomy has been thought to facilitate the development of SLE in patients with MG.2–4,6–9 Although trigger factors to both of them are not well understood, they may share certain mutual environmental, genetic and immunological aetiologies. We met a man who was previously recognised to have MG and subsequently developed lupus nephritis after a thymectomy. The 48-year-old man was recognised to have generalised type of MG at the age of 21. Initial presentations included limb weakness, dysphagia, dysarthria and eyelid lag. Elevated anti-acetylcholine receptor (AchR) antibody titres along with a positive Tensilon test and a 3-hertz repetitive stimulation test established the diagnosis. He received pyridostigmine soon after and underwent total thymectomy 2 years later because of respiratory distress. There was no thymoma in the dissected tissue. MG was subsequently controlled uneventfully with pyridostigmine alone for 23 years until muscle weakness recurred. For this recurrence, mycophenolate mofetil (MMF) was added with good response. However, proteinuria (>500 mg/day) developed in the following year despite regular medication. There was no associated medical condition such as diabetes mellitus, hypertension or any other concomitant medication that could account for the development of proteinuria. Urinalysis showed occult blood, dysmorphic erythrocytes and proteinuria. Meanwhile, two episodes of pyogenic renal abscess, which were caused by Klebsiella pneumoniae and extended-spectrum β-lactamases (ESBL)Escherichia coli, respectively, as confirmed by magnetic resonance imaging, sonography-guided aspiration and bacterial cultures, resulted in acute renal failure that required temporary haemodialyses even after systemic antibiotic treatment. Autoantibody screening was performed because of these unusual manifestations in a long-termMG. These investigations showed high titres of antinuclear antibodies (ANA) and antibodies against double-stranded DNA (dsDNA), increased titre of anticardiolipin antibodies but failed to show anti–neutrophil cytoplasmic antibodies (por c-ANCA). There were also low complement C4 titres and high erythrocyte sedimentation rate (ESR). These serological features suggested the association of lupus nephritis. Because of a refusal of renal biopsy by the patient, oral methylpredenisolone (8 mg/day), in addition to pyridostigmine and MMF, was provisionally given, which seemed very effective. Transient pleurisy with small amount of pleural effusion was also observed during the subsequent disease course, which resolved quickly after increasing steroid doses. He toleratedMMFwell without major adverse effects and is currently in remission state ofMGbut the small amount of proteinuria persists. Normalisation of C4 concentrations, ESR, haematuria and decrease in anti-dsDNA antibody titre, as well as SLE Disease Activity Index (SLEDAI) score, were also observed at regular follow-up. Interestingly, family correlation has been found in this patient. His younger sister, also with MG at the age of 20 and undergoing thymectomy, developed lupus nephritis 5 years after the surgery. However, she died of untreated lupus nephritis at the age of 35. The patient has definitely developed SLE in the late course of his disease. Although ANA and antidsDNA antibodies may appear in patients with MG such as ours, proteinuria and recurrent bacterial renal abscess in the absence of anatomic defect of the urinary tract are unusual in this organ-specific autoimmune disorder.MG is an autoimmune neuromuscular disease with a feature of impaired neurotransmission led by the AchRs and/or, less frequently, a musclespecific tyrosine kinase (MuSK) involved in AchR clustering.10 The B-cell chemoattractant of CXC chemokine, CXCL13, was recently found to be a key molecule in autoimmune MG. Meraouna, et al.11 have described a high CXCL13 production by thymic epithelial cells in patients with MG, which could be inhibited by glucocorticoids. Thymectomy induces a decrease in serum CXCL13 concentration with clinical improvement. Thus, CXCL13 is probably responsible for B-cell attraction and ectopic germinal centre formation in the thymus. A similar result has also been obtained by us using antibody array detection Lupus (2008) 17, 860–861