|Year : 2013 | Volume
| Issue : 3 | Page : 133-135
Juvenile ocular myasthenia gravis in association with thymolipoma
Kavita Mardi, Neha Bakshi
Department of Pathology, Indira Gandhi Medical College, Shimla, India
|Date of Web Publication||22-Nov-2013|
12-A, Type V Quarters, IAS Colony, Kasumpti, Shimla, H.P
Thymolipomas are uncommon tumors of anterior mediastinum. Their association with juvenile ocular myasthenia gravis is extremely rare. A 14-year-old boy presented with ptosis of 2 years and left-sided diplopia of 19 months duration. On examination external ophthalmoplegia and ptosis were present. Generalized muscle weakness was absent. On a neostigmine challenge test, the boy showed improvement in symptoms after 20 minutes of neostigmine injection. Anticholinesterase antibodies and antinuclear antibodies were negative. Chest CT revealed a soft tissue mass in the anterior mediastinum. Histopathological examination of the excised mass was diagnostic of thymolipoma.
Keywords: Juvenile, myasthenia gravis, occular, thymolipoma
|How to cite this article:|
Mardi K, Bakshi N. Juvenile ocular myasthenia gravis in association with thymolipoma. Sahel Med J 2013;16:133-5
| Introduction|| |
Thymolipomas are rare tumors accounting for up to 9% of all thymic tumors.  They are uncommonly associated with Myasthenia gravis (MG).  However, juvenile ocular myasthenia gravis associated with thymolipoma is extremely rare.  We report one such rare occurrence in a 14-year-old boy.
| Case Report|| |
A 14-year-old boy presented with left-sided diplopia since 19 months and ptosis since 2 years. There were no complaints of dysphagia or difficulty in breathing. On examination external ophthalmoplegia and ptosis were present. These ocular signs and symptoms, especially ptosis, were made worse by bright light. Generalized muscle weakness was absent. On a neostigmine challenge test, ptosis and diplopia improved after 20 minutes of neostigmine injection. Anticholinesterase antibodies and antinuclear antibodies were negative and serum CPK levels - 50 μm/l.
A diagnosis of Juvenile ocular myasthenia gravis was made. Chest X-ray showed no mediastinal abnormality. However, chest-computed tomography (CT) showed a soft tissue mass in the anterior mediastinum with smooth margins, fat attenuation, and soft tissue strands. A radiological diagnosis of thymoma was given. The patient underwent extended thymectomy for the relief of symptoms. Histological examination showed a well-circumscribed lesion comprising islands of thymic tissue dispersed among adipose tissue, resulting in the effacement of lobular architecture of thymus [Figure 1].These islands of thymic tissue were showing involutional changes with frequent cystic degeneration of Hassall's corpuscles and dystrophic calcification [Figure 2]. These histological features were diagnostic of thymolipoma. Symptoms of ocular myasthenia gravis were improved after the operation.
|Figure 1: Photomicrograph revealing islands of thymic tissue dispersed among adipose tissues (H&E, 20×)|
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|Figure 2: Higher magnifi cation revealing frequent cystic degeneration of Hassall's corpuscles and dystrophic calcifi cation (H&E, 40×)|
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| Discussion|| |
Thymolipomas are rare tumors of the anterior mediastinum accounting for up to 9% of all thymic tumors. , They are benign neoplasm composed of mature adipose and thymic tissue. These tumors are associated with autoimmune diseases in up to 50% of the patients, including myasthenia gravis, aplastic anemia, hypogammaglobulinemia, lichen planus, and Graves' disease.  Less than 200 cases have been described in the literature.  Myasthenia gravis (MG) is generally associated with and present in up to 30% of thymomas.  However, association with thymolipomas is uncommon, with less than 25 cases reported in the world literature. 
Thymolipomas with MG usually appear in older patients (40-50 years). , Juvenile ocular myasthenia gravis associated with thymolipoma is extremely rare. The association of MG with thymolipomas is uncommon, and it is regarded by some authors as a simple epiphenomenon, although the fact that symptoms regress in most patients after thymectomy suggests that there is a relationship. The pathogenesis of thymolipoma is not clear. , One of the theories considers that the thymolipoma is a fatty involution of a thymoma, and therefore the thymolipomas would be true thymomas. Furthermore, the coexistence of thymolipoma with MG, other autoimmune diseases, or neoplastic conditions suggests that thymoma and thymolipoma are at least related tumors.
The patients with thymolipoma and MG differ from patients without MG in two ways: (1) thymolipomas with MG appear in older patients (20-30 years vs. 40-50 years)  and (2) mean thymolipoma weights are lower in patients with MG (100 g vs. 1000 g).  This can be explained because thymolipomas without MG are usually diagnosed when they are large. A very small thymolipoma may be associated with myasthenia gravis even if the content of though thymic tissue is low. 
Prepubertal children in particular have a higher prevalence of isolated ocular symptoms, lower frequency of acetylcholine receptor antibodies, and a higher probability of achieving remission. Ocular myasthenia gravis (OMG) is, by definition, MG restricted to the oculomotor muscles for 2 years without becoming generalized. Case series have reported lower rates of generalization in children than those in adults.  Progression may be even less frequent in prepubertal children.  Patients without antibodies to AChR or MuSK are described as having seronegative myasthenia gravis (SNMG). Some of these children who are negative for AChR antibodies will have "low affinity" antibodies to the AChR which were not detectable using the standard assays.
These cases of SNMG should be distinguished from congenital myasthenic syndromes (CMS) as the treatment options, prognosis, and genetic implications are very different. CMS usually present in the first years of childhood with variable disability. There is often a positive family history, and diagnosis is aided primarily by electrophysiology and DNA analysis and occasionally by muscle biopsy. Patients of with autoimmune disease symptoms occasionally show an improvement of the symptoms after a resection of the tumors. There was marked improvement in the signs and symptoms after the excision of the thymolipoma in our patient also.
In conclusion, though thymolipomas are uncommon tumors, they can be associated with myasthenia gravis. This case report establishes the extremely rare association of juvenile ocular myasthenia gravis with thymolipoma. Thus, thymolipomas should be considered in the differential diagnosis of mediatinal tumors associated with myasthenia gravis.
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[Figure 1], [Figure 2]