BACKGROUND: Myasthenia gravis (MG) is an autoimmune disease which mainly affects neuromuscular junctions. The ages, modified Osserman classification and clinical manifestation and humoral immunol function of MG with and without thymic abnormality are different.OBJECTIVE: To explore the clinical manifestation and humoral immuno-function of MG with abnormal and normal thymus gland.DESIGN: Contrast observation.SETTING: Department of Neurology, the Third Affiliated Hospital of Sun Yat-sen University.PARTICIPANTS: A total of 49 inpatients with MG were selected from the Third Affiliated Hospital of Sun Yat-sen University from March 2000 to August 2005. All the patients had typical clinical manifestation of MG and positive neostigmine test. All the patients knew and agreed the laboratory examinations. There were 22 males and 27 females of 2-69 years old. Chest MRI or CT scan were performed to reveal thymus gland abnormality. According to whether there was tumor in superior mediastinum, all patients were divided into 2 groups, abnormal and normal groups. Normal thymus gland group (n=30) contained 16 males and 14 famales of 6-43 years old. Abnormal thymus gland group (n=19) contained 6 male and 13 female of 2-69years old.METHODS: ① All patients were questioned about initial symptoms. Meanwhile, main clinical manifestations were recorded at hospital admission. ② 7180A automatic biochemical analyzer and automatic microplate reader were used in detecting seroimmunity index. The levels of C3, C4, IgG, IgA, IgM and CH50 in blood serum were analyzed by nephelometry. ③ Clinical classification is based on modified Osserman classification. The patients with MG were divided into six types: Ⅰ (Ocular myasthenia), Ⅱ a (Mild generalized myasthenia), Ⅱ b (Moderately severe generalized myasthenia), Ⅲ (Acute fulminating myasthenia), Ⅳ (Late severe myasthenia).MAIN OUTCOME MEASURES: ① Differences of initial symptoms and clinical manifestation of two group patients. ② Differences of age of onset and modified Osserman classification of two groups. ③ The humoral immuno-functions of two groups were compared.RESULTS: All the 49 patients were involved in the final analysis of results. ① Differences of initial symptoms: Ptosis was the most common initial symptoms in both groups. Patients with ptosis of normal thymus gland were 25 (83%, 25/30). Patients with ptosis of abnormal thymus gland were 13 (68%, 13/19). Patients with normal thymus gland: dysphagia 2 (7%, 2/30), diplopia 4 (13%, 4/30), fatigue 4 (13%, 4/30), dysarthria 3, (10 %, 13/30). Patients with abnormal thymus gland: dysphagia 3 (16%, 3/19), diplopia 6 (32%, 6/19),fatigue 3 (16%, 3/19), dysarthria 2 (10%, 2/19). ② Differences of clinical manifestation of two groups: Ptosis was the most common clinical manifestation in both groups. Patients with ptosis of normal thymus gland were 29 (97%, 29/30). Patients with ptosis of abnormal thymus gland were 15 (79%, 15/19). The rates of fatigue and breathing disorder in patients with abnormal thymus gland were higher than patients with normal thymus gland. Myasthenia crisis occurred in 3 patients (16 %, 3/19) in abnormal thymus gland group, with 1 (3%, 1/30) in abnormal thymus gland group. ③ Differences of age of onset and modified Osserman classification: The rate of type Ⅰ (63%, 19/30) in patients with normal thymus gland was higher than patients (42%, 8/19) with abnormal thymus gland. The rates of type Ⅱ a, Ⅱ b and Ⅲ (58 %) in patients with abnormal thymus gland were higher than patients (37%, 8/19) with normal thymus gland. But no differences were found between two groups (P ＞ 0.05). Patient number of onset from 20 to 29 year old in abnormal group (47%) was higher than that in normal group (20%). Comparison of two groups was x2=4.10 and P ＜ 0.05.④ Comparison of the humoral immunol indexes of two groups: The levels of IgG, IgA, C3 and CH50 in abnormal group were higher than those in normal group. But no differences were found between two groups (P＞ 0.05).CONCLUSION: ① Ptosis was the most common initial symptom and clinical feature in both groups. ② Clinical manifestation in abnormal group were more severe, and ages of onset in abnormal group were more young. ③ The humoral immuno indexes of two groups were not significantly different.