Hi, thanks for sharing your health concerns with HCM!
Dear, If I were your treating Doctor for this case of a hard lump on your arm, I would come up with three possibilities, these include:
1. a bursa or collection of thin pus/
synovial fluid due to some irritative pathology or
ganglion cyst!
2. The second possibility is of benign and simple conditions like
lipoma or neurofibroma; there is nothing to worry about these!
3. The last possibility is of sebaceous cyst or some other cysts like parasitic cyst!
This is enlarging in size but I don't think it to be a lymph node, as per my needle
biopsy experience; It NEEDS TO BE REMOVED SURGICALLY, I FEEL!
I suggest you to go for an FNAC and
ultrasound of the lump for confirmation and to relieve your concerns!
Hope this answers your question. If you have additional questions or follow up questions then please do not hesitate in writing to us. I will be happy to answer your questions.
Wishing you good health.