Hello,
Welcome to healthcare magic.
Thank you for your query.

Only elevated IgM or monoclonal gammopathy has various causes.
The common causes are hematological malignancy(lymphoma, myeloma), connective tissue disorder(rheumatoid arthritis, polymyalgia rheumatica),infection(HIV), amyloidosis, solid tumors etc.
In addition, they may be present with no underlying disease.

I think that you are free from these disease.
Because in idiopathic pulmonary fibrosis, the IgM level may be increased non specifically & you are suffering from this disease. It is more likely the cause in you.

But it is better to exclude other possibility.

Consult your doctor for get examined & relevant investigation.

I hope I have been some help of your query.
Please write if you have any doubt.
Take care.

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