The various autoimmune diseases that occur in patients with thymoma include mainly myasthenia gravis (MG), pemphigus, systemic lupus erythematosus (SLE), pure red cell aplasia (PRCA), and other conditions that seldom appear concomitantly with this tumor.
MG is an autoimmune disease resulting from the production of antibodies against the acetylcholine receptor of the muscular endplate , Only about one-third of the patients with thymoma have MG, while 10-15% of myasthenic patients have a thymoma. MG patients with thymoma are usually older than 40 years of age, have high antibodies titer and a poor clinical response to thymectomy, whereas MG patients with thymic hyperplasia (which is more frequently found in MG than thymoma) can be either older than 40 years of age with low titer of antibodies and poor response to thymectomy, or younger than 40 years of age, with moderate antibodies titer and a good response to thymectomy. In addition, there is an increased prevalence of autoimmune diseases in MG patients, mainly among those with thymic hyperplasia rather than in those with thymoma .
Pemphigus refers to a group of autoimmune blistering diseases of the skin, in which the epidermal cell adhesion is lost , due to the formation of autoantibodies against desmosomal transmembrane glycoproteins in the stratified squamous epithelia . The association between pemphigus and cancer has long been postulated. In a case series published in 1974,12% of the total cases of pemphigus were found to have associated internal malignancies , and in two recently published case series [8-9] the association ratio of internal malignancies with pemphigus was 5.0%. In addition, 54% of the patients with pemphigus who developed a neoplasm were reported to have a malignancy of the lymphoid or reticuloendothelial system . Nonetheless, pemphigus has also been reported with solid tumors of all organs . Pemphigus was found to appear before or after the resection of neoplasm with equal frequency .
Thymoma is one of the neoplasms associated with pemphigus. Pemphigus vulgaris is more common in patients with nonthymic neoplasms, whereas in patients with thymoma, it is as common as pemphigus foliaceus . However, Souteyrand et al.  have previously reviewed 20 cases of patients with thymoma and pemphigus, and in their report pemphigus erythematosus was the predominant type (55% of the cases). Interestingly, patients with nonthymic neoplasms usually have pemphigus before the detection of malignancy, whereas the majority of patients with thymoma have it before the development of pemphigus . Since thymoma is associated with other autoimmune conditions as well, it is not surprising that many of pemphigus patients have additionally another autoimmune disease. Most of the cases of pemphigus associated with thymoma and another autoimmune disease are summarized in a review by Patten and Dijkstra . A recently published case report, that is not included in this review, deals with a patient who was found to have thymoma, pemphigus erythematosus and systemic lupus erythematosus .
SLE is only rarely found in patients with thymoma, usually it is found before the diagnosis of thymoma, and in older patients than those with only SLE  are. However, SLE is more common in patients with MG than in patients with thymoma, and hence once chronic fatigue is found in SLE patients, MG should be included in the differential diagnosis ,
PRC A is found in 5-10% of patients with thymoma , and there are also reports of patients with the triad of PRCA, MG and thymoma. PRCA is considered as an autoimmune condition that involves either humoral (a serum IgG erythropoietic inhibitor)
or a cellular component (T cell capable of inhibiting erythropoiesis). In addition, there are also several reports of autoimmune hemolytic anemia associated with thymoma (reviewed in ).
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