How to Tell Madelung from Regular Lipoma?

It will probably be in your best interest to have the symptomatic lesions excised and evaluated pathologically. If this is done by a well experienced pathologists,  he/she may be able to differentiate lipoma from the cutaneous lesions associated with benign symmetrical lipomatosis (Madelung's).

Best wishes.

GREAT QUESTION.
Hard to tell without an examination.
Madelung's disease (aka multiple symmetrical lipomatosis, cephalothoracic lipodystrophy, and the Launois-Bensaude syndrome) frequently appears in association with alcoholic liver disease, "low blood" count with fewer but big red blood cells and disorders of the peripheral nervous system. It has been associated with alcoholism.
FROM http://emedicine.medscape.com/article/1057855-overview :
Diffuse congenital lipomatosis
Diffuse poorly demarcated lipomas localized primarily on the trunk characterize this type (see Media File 1).
Tumors often infiltrate through muscle fibers, making them resistant to surgical removal. These tumors are composed of immature fat cells.
Benign symmetric lipomatosis (Madelung disease)
Madelung described the condition in 1888.
Lipomas of the head, neck, shoulders, and proximal upper extremities characterize this condition.
Men are affected 4 times as often as women.
The patient's history often includes excessive alcohol consumption or diabetes.
Other conditions associated with Madelung disease include malignant tumors of the upper airways, hyperuricemia, obesity, renal tubular acidosis, peripheral neuropathy, and liver disease.
Familial multiple lipomatosis
This clinical entity is characterized by few-to-many, small, well-demarcated, encapsulated lipomas that commonly involve the extremities.
Typically, this form appears during or soon after adolescence.
The neck and shoulders usually are spared (unlike benign symmetric lipomatosis).
A family history of multiple lipomas usually exists, and an autosomal dominant mode of inheritance is found.
Dercum disease (adiposis dolorosa)
Painful lipomas are the hallmark of this rare condition.
Lipomas typically occur on the extremities of obese postmenopausal women.
Alcoholism, emotional instability, and depression commonly are associated with Dercum disease.
Angiolipomas
Typically, these tender, soft, subcutaneous nodules are present in adolescence.
Tumors frequently are multilobulated and are somewhat firmer than ordinary lipomas.
The associated pain is vague and may be spontaneous or caused by pressure.
Hibernomas
Tumors are solitary well-circumscribed nodules that typically are asymptomatic.
Usually, tumors are located in the interscapular region, axillae, neck, or mediastinum.
Histologically, hibernomas are composed of embryonic brown lipoblasts termed mulberry cells because of their appearance.
I would excise one and get a good pathologist to look at it and work you up to make sure you are otherwise in good health and do not have any of these associated disorders.
Good Luck.

Madulung's Disease or Benign Symmetric Lipomatosis does not consist of true lipomas.
When I perused my pathology tomes, including those devoted to Soft Tissue Pathology, Madulung's was not listed as a form of lipomas but as a lipomatosis.
Experts regard it more as a metabolic condition rather than true tumors. The fatty tissue in Madelung's is not enclosed within a capsule like lipomas. Lipomas have discrete borders, small ones can be "shelled out" in a simple office procedure. One cannot do that with Madelung's.
Madelung's is also remarkable in its absolute symmetry. Patients with Madelung's demonstrate a growth of fatty masses around the face, back of the head, neck, upper arms, abdomen, back and upper leg in a symmetric and very typical pattern.
It is most likely that this is a more common condition than most people realize since many people with it are assumed to just be getting fat.
What makes this a metabolic problem rather than just the growth of lipomas is that there are a number of endocrine like challenges that co-exist with Madelung's. Often patients will have neurologic deficits such as weakness or paraesthesias ( crawling or tingling sensations) and areas of anesthesia (decreased sensory feeling, The autonomic nervous system is turned on its head with unusual flushing, and sweating, often gustatory (during eating), and wide fluctations in blood pressure and pulse.
Frequently, there is a diabitic componet with glucose intolerance and ulcers on the soles of the feet.
As you pointed out many of patients with Madelung's are alcoholic and perhaps, alcohol unmasks a prior genetic tendency. Maybe if there was more alcoholism there would be more cases of Madelung's.
The diagnoisis of Madelung's can be made by observing the symmerty of the lipomatosis, a history of weight gain, even in the face of dieting, extreme fatigue and muscle achiness, unexplained pain over the muscles, hypersensitivity to touch or minor trauma, weakness of the extremilties, and severe unexpolained cramping over the sites where the lipomatous masses most commonly occur.
I hope this helps.