You will tend to notice a tender swelling in the hollows normally found between the patella and the lower leg. As the discomfort may be worse after runs, it may limit training.
Your doctor will see exactly the same as yourself, although he may be more expert than you at eliciting tenderness!
As the diagnosis is often obtained from the history and requires little in the way of investigation, a detailed training history is important. It is an over-use injury, more noticeable at the end of a run or if you have increased your mileage too quickly. A sudden switch to hill training may bring it on.
What else could it be?
All the other causes of anterior knee pain may need to be eliminated, such as patellar problems, and cartilage tears and strains, as well as arthritis and internal damage, which produces fluid on the knee.
Rest, ice and anti-inflammatories with training modification may well be sufficient to settle the problem.
If physiotherapy, usually in the form of ultrasound, fails to settle Hoffars syndrome, a cortisone injection will usually suffice. A need for surgery is unlikely.
Can you run through it?/Recovery time
Training modification and sticking to sensible terrain may well be all thats required, and some athletes dont let it interrupt the flow of their training.