Answer: Unfortunately there are many possible causes ranging from the room being too hot or too cold or the air too dry to under or overwatering to possibly an insect problem such as scale. You might review the care instructions in the following article and see if any environmental factors might be causing it. At this time of year, low light combined with dry indoor air and overly warm room temperature can cause leaf drop. You may need to cut and paste the complete url into your browser to make it work correctly.
I hope this helps you trouble shoot.
Q&A Library Searching Tips