Thick neck is usually caused by thyroid diseases, when the thyroid gland becomes enlarged or has lumps, it will be manifested as thick neck, such as simple goiter, hyperthyroidism, thyroid tumor and so on. 1. Simple goiter: caused by increased demand of thyroxine and iodine deficiency. The thyroid gland will be enlarged to different degrees, i.e. manifested as a thick neck. 2. Hyperthyroidism: a disease of generalized hypermetabolism caused by abnormal increase of thyroid hormone, manifested by diffuse enlargement of thyroid gland, i.e., thick neck, accompanied by symptoms such as protruding eyes, emaciation, and impatience. 3. Thyroid tumor: including papilloma, follicular adenoma, medullary carcinoma, etc. The most common clinical manifestation is that lumps are found in the thyroid gland, which can cause respiratory difficulty, dysphagia, blood and other symptoms. If you have a thick neck for a long period of time, you should consult a doctor in time and undergo relevant examinations to find out the cause of the disease.