Interstitial renal diseases affect the tubules. Most commonly you're talking about Interstitial Nephritis, but technically you could include all the inherited diseases that affect this region too, including the cystic diseases and some other interesting but less common conditions. Read a brief introduction to Interstitial nephritis in the Edren Textbook if you need, or consider the very short lecture below.
Tubulointerstitial diseases (13 mins lecture with commentary. Requires Flash) Runs on naturally from Glomerular diseases. Recommended music for this lecture is Harlem Nocturne (unknown artists, Toronto). Recommend you play that in a separate window at half volume.