Signs of upper respiratory disease can vary from mild airway noise to severe distress with heat and exercise intolerance. In some cases it can even lead to death. Brachycephalic airway syndrome is a well-recognized condition in brachycephalic dogs (dogs with "pushed-in" noses). 

In the case of Norwich Terriers, evidence shows that there are changes in the larynx that are not seen in brachycephalic dogs. In Norwich Terriers it is likely that upper airway syndrome is a separate and different condition from brachycephalic airway syndrome. While breeders have long known of upper airway issues in Norwich Terriers (NTUAS), veterinary awareness and recognition of NTUAS has lagged behind.

Dr. Bryden Stanley - a board certified veterinary surgeon - explains the clinical signs and possible anatomical abnormalities seen in Norwich Terriers with upper airway syndrome: