Good Morning and welcome. I am Dr. Loretta, a licensed veterinarian and I am happy to answer your question.
Most diseases will cause hair loss and not what you are describing....this excess fur in tufts could be due to a hormonal issue such as a thyroid problem or a metabolic issue such as Cushings disease. I would recommend that you take Lewis to your vet for blood work and an exam....I Believe testing will tell your vet what is causing this odd fur accumulation. You will not know until the tests are run.
Cushings disease is caused by excess steroid hormones being produced and there are treatments for this. This LINK will explain in more detail.
Does that make sense to you?
Please let me know if you have ANY other questions. My goal is to give you 100% satisfaction and if you are not yet satisfied, please Reply so I can clarify for you
Sincerely, Dr. Loretta