Familial multiple lipomatosis (FML) is a rare adipose disorder (RAD) of multiple lipomas in subcutaneous fat.  FML is usually inherited in an autosomal dominant manner with males and females being equally affected, though men are reported in some families to be affected more than females.  Some members in an FML family may have only a few lipomas whereas others may have hundreds to thousands; it is not understood why there is unequal penetrance.  In some families, the lipomas can be angiolipomas (lipomas where blood vessels dominate), in others only lipomas and still others with a mixture of the two.  Lipomas usually are not tender (angiolipomas are tender) except in some cases where they can be tender while growing.  They may also cause a slight feeling of itching or burning. Some lipomas can be tender if they develop in areas of pressure such as on the back of the legs, on the low back (pressure from a chair) or on the lateral wrist due to the use of a computer mouse.  Multiple trauma to an area can cause growth of the lipomas.  FML has been associated with multiple nevi.

The pathophysiology of the lipoma growth is not known. Morphologically, subcutaneous angiolipomas contain two types of mesenchymal tissue, adipose and vascular tissue.  Angiolipomas also have normal karyotypes as opposed to other lipomatous lesions(1) similar to 28 benign hemangiomas that have been  karyotyped.  Angiolipomas therefore, suggest an underlying vascular problem with a secondary growth of adipose tissue.

There also may be lymphatic dysfunction in FML since so many genes are shared between lymph and blood vessels. When a defect presents in a blood vessel, it will leak leading to hypoxia then the blood vessel will signal for the growth of new vessels.  Fat grows to support the new blood vessel growth as does connective tissue.  The more fluid, the more fat and connective tissue to the point where lipomas are connected in a web, and that web and the lipomas connect to other nearby structures like muscle and bone. 

One goal for people with FML would be to avoid trauma or inflammation to the subcutaneous fat.  The lipomas are most likely restricted to subcutaneous fat.  However, Dr. Francis X. Dercum described an obese man with multiple lipomas and multiple hormone deficiencies that had some on organs.  Another goal would be to maintain a normal body habitus to decrease inflammation in the body overall (inflammation increases with increasing weight).

References

1. Sciot R, Akerman M, Dal Cin P, De Wever I, Fletcher CD, Mandahl N, et al. Cytogenetic analysis of subcutaneous angiolipoma: further evidence supporting its difference from ordinary pure lipomas: a report of the CHAMP Study Group. Am J Surg Pathol. 1997;21(4):441-4.