We viewed your photos.  We do not have a lot of experience with cedars.  They do not have a lot of problems with disease and insects.   Some cultivars are very susceptible to cold and have hardiness issues.  They prefer a well drained and somewhat dry, sunny location and protection from sweeping winds.  You may be dealing with environmental issues but we cannot say for sure.

It is possible that the tree may be affected by its location.  The roots may be confined in the narrow strip where the tree is planted and surrounded by sidewalk and driveway.  Heat and drought may also be factors which can affect the root system.  Also, the tree may be a challenge to keep in bounds as it gets larger.

It looks like the brown needles are on old growth. Monitor the tree this spring and look for new growth.  All you can do is keep watered during dry periods and make sure mulch is no thicker than several inches and keep away from the base of the trunk.  You can send more photos if you additional symptoms this growing season.

mh

This tree was planted in 2003 so it is 15+ years old.  It's possible the roots are feeling cramped but I would think the whole plant would show that effect. Would microscopic examination of the affected needles be informative?

Thank you for the additional information.  This has been a long, cold winter and as mentioned above this plant can be susceptible to environmental issues.   
 In general most blights are on new needles.  The browning in your photos looks like old growth.  At this point we recommend that you monitor for new growth and send us photos if you see additional symptoms.  We do not take plant samples.  

mh