Which one of the following is closely associated with Myasthenia gravis?

(A) Thymoma # MYASTHENIA GRAVIS is a neuromuscular disorder characterised by weakness and fatigability of skeletal muscles.> Up to 75% of patients have an abnormality of the thymus; 25% have a thymoma, a tumor (either benign or malignant) of the thymus, and other abnormalities are frequently found.> The disease process generally remains stationary after thymectomy (removal of the thymus).# Disorders Associated with Myasthenia Gravis & Recommended LaboratoryTests> Associated disorders Disorders of the thymus: thymoma, hyperplasia Other autoimmune disorders: Hashimoto's thyroiditis, Graves' disease, rheumatoid arthritis, lupus erythematosus, skin disorders, family history of autoimmune disorder> Disorders or circumstances that may exacerbate myasthenia gravis: hyperthyroidism or hypothyroidism, occult infection, mec ical treatment for other conditions (aminoglycoside antibiotics, quinine, antiarrhythmic agents)> Disorders that may interfere with therapy: tuberculosis, diabetes, peptic ulcer, gastrointestinal bleeding, renal disease, hypertension, asthma, osteoporosis, obesity# Recommended laboratory tests or procedures> CT or MRI of mediastinum> Tests for lupus erythematosus, antinuclear antibody, rheumatoid factor, antithyroid antibodies Thyroid-function tests PPD skin test Chest radiography Fasting blood glucose measurement Pulmonary-function tests Bone densitometry in older patients