Hi Lara - understand because this is new to me, too...

Excerpts from a paper on the OC Foundation Organization website
http://www.OCFoundation.org/hoarding/about-hoarding/hoarding-where-does-it-belong.php




Dr. Claiborn did review of the literature and saw patterns of research findings:

Hoarding is typically thought of as a symptom of OCD. However, there are several ways in which it is distinct.

• For instance, in hoarding it is difficult to identify an intrusive thought that is typical of other obsessive symptoms.
• Also, hoarding does not respond as well to treatments that are effective for other OCD symptoms (see Steketee & Frost, 2003).
• Furthermore, recently researchers have attempted to identify subtypes of OCD based on the types of obsessions and compulsions experienced. This research has consistently found hoarding to fall into a separate cluster (Calamari, Wiegartz & Janeck, 1999; Summerfeldt, Richter, Antony & Swinson, 1999).
• Hoarding and tics also show up more commonly in the families of people who hoard than those of other OCD patients.
• This might suggest a separate genotype (inborn differences in our genes - OMT) (Samuels et al., 2002; Stein et al., 1999).
• If this is true, it could be that OCD hoarding represents a separate disorder that might explain the poor response to treatments (Saxena et al., 2002).
• Another possibility is that hoarding is one of a spectrum of disorders related to OCD - but somehow distinct (Stein, Seedat, & Potocknk, 1999).
• Investigators have suggested a wide range of disorders as part of this spectrum including hypochondriasis, eating disorders, and many more.
  
  

Is hoarding an impulse control disorder rather than OCD?

Among the spectrum of disorders thought to be related to OCD are the impulse control disorders. These disorders are characterized by the failure to control the impulse to engage in harmful behavior, for example "compulsive gambling," kleptomania, etc.

The excessive acquisition of new possessions that characterizes compulsive hoarding fits this characterization. This behavior mimics what is usually called "compulsive shopping."

Although not officially recognized as a disorder in DSM-IV, compulsive shopping is often considered an Impulse Control Disorder ....
and resembles (or is co-morbid with) other OCD spectrum disorders (Koran, 1999).

Hoarding individuals may purchase excessively, or may acquire excessive amounts of free items, or may pick from others' trash.

Compulsive hoarding (generally) has enough in common with other forms of OCD to be classified as a variation of this disorder with some features of impulse control disorders.

This particular variety of OCD is common and can be severe and quite difficult to treat.

Ultimately, research may clarify questions about differences in neurobiology or genetics of varieties of OCD and tell us where hoarding best fits.

(boldface & emphasis added by me - click on link above to see full article)