Frequency and clinical correlates of vitiligo in myasthenia gravis.

Abstract

Sirs: Myasthenia gravis (MG) can be accompanied by several disorders, especially those presumed to be autoimmune in origin. Although the association of MG and vitiligo has been described well in the literature [5], only four case reports have been published [1, 7–9]. In all these, the authors suggest a possible underlying autoimmune basis for both diseases. However, because vitiligo is a common skin disorder that affects approximately 0.5 to 2% of the general population [6] with its aetiology still unproven [4], the question of whether simultaneous vitiligo and MG represent a coexistence or true association has yet to be answered. Therefore, we undertook this first methodical study to elucidate the frequency and clinical correlates of vitiligo in patients with MG. Over the past 12 years we have examined and treated 202 patients with MG (male/female ratio 71/131). Their ages varied from 1.9 to 77 years with a mean of 32. The diagnosis of MG was made by typical symptoms and signs, positive responses to edrophonium chloride, decremental pattern during repetitive nerve stimulation, and elevated levels of antiacetylcholine receptor antibody titres [2]. Eighty-three of the 202 patients had ocular symptoms only, while the other 119 patients had generalized symptoms. Chest computed tomography (CT) was performed in all patients. A thymoma was looked for pathologically in 110 of the 119 patients with generalized MG who underwent extended thymectomy [2]. Thirty-five patients had a thymoma verified by pathology. Of the 202 patients, only 1 (0.5%) had vitiligo over the regions involving face and distal portions of the four limbs. This 46-year-old woman had had mild ocular signs since the age of 9 years. Vitiligo developed at age 36 years and gradually increased in number and size of lesions while her myasthenic symptoms subsided spontaneously. Her thyroid function was normal, although the result of antimicrosomal antibody test was positive, and her mother and aunt had overt hyperthyroidism. Chest CT revealed no thymic mass in the mediastinum. Treatment with oral glycyrrhizin (225 mg/day), carponium chloride ointment, and corticosteroid cream resulted in a gradual recovery from her skin lesions. Vitiligo is an acquired melanin pigmentary disorder manifested by expanding depigmented lesions of the skin. To date, the mechanism of vitiligo has not been convincingly elucidated, and a number of hypotheses, including biochemical, neural, and autoimmune hypotheses, coexist with equal likelihood [4]. Because vitiligo is associated with autoimmune disorders such as thyroid disease, adrenal insufficiency, and diabetes mellitus, the autoimmune hypothesis has occasionally been proposed. However, our current study revealed a rather low frequency (0.5%) of vitiligo in 202 patients with MG, suggesting that the association between MG and vitiligo may be infrequent. The low frequency of vitiligo in our study is comparable to the frequency in the general population [6]. Cruz et al. [1] reported that only 1 of over 60 MG patients (under 1.7%) who also had thyroiditis developed vitiligo. A recent study by Schallreuter et al. [6] showed a low frequency of autoimmune disorders in 321 patients with vitiligo; those with thyroid disease were the one exception to this rule. In their series no patient with MG was found. Our patient had thyroid antibodies and a positive family history of hyperthyroidism, a finding compatible with the assumption that vitiligo is closely associated with autoimmune thyroid disease [6]. Because both MG and vitiligo are frequently associated with thyroid disease, a possible genetic factor closely linked with thyroid disease may explain the coexistence of the two disorders. In our patient no clinical correlation was found between MG and vitiligo, consistent with the previous report [1, 7–9]. With regard to treatment, systemic corticosteroid was reportedly beneficial against vitiligo in 1 patient [7]. In conclusion, we found a low frequency (0.5%) of vitiligo in patients with MG. This result contrasts with the other skin disorders accompanying MG, pemphigus and alopecia areata, which have an apparent relationship with MG and thymoma [3].