The causes can be varied.

Thyroid disorder should be looked for and to be treated if present.

Any other obvious co-existing gynaecological cause to be ruled out.

A patient with metabolic syndrome and irregular cycles is likely to benefit from life style modification, weight loss and metformin.

Firstly-life style modification (regulation of BMI), and next are dosage of hormones, detection of insulin-resistence/ intolerans of glucose etc.

High insulin drives overproduction of androgens at the expense of progesterone, in the ovaries, by upregulation of the 17,20-lyase system.  I've seen a handful of people who also overproduce progesterone, but more often than not, if you profile these women throughout an entire cycle, via saliva, you see a diminished or absent progesterone surge.  Giving a small amount of progesterone for the 2nd half of the cycle often helps re-regulate these women.  In a small percentage it will elevate androgens, so you have to start low and go slow: 5-10 mg qd topically 14 days/month. It doesn't fix the underlying problem, but a little bit of progesterone can work wonders. 

If there's no selenium in the diet, conversion of T4 to T3 in the ovary won't be optimal. The ovary won't make Pg if it can't get any local T3 formation; it won't respond to LH.  (Ditto males: guys won't make testo in response to LH if they can't make T3 in the testicles.)

Alot of these women are overloaded with estrogens due to overproduction of androgens/androgen precursors, so anything you can do to increase fecal excretion is helpful: increased fibre intake, calcium-glucarate (to avoid de-conjugating estrogens in the colon).  Zinc supplementation will also help to downregulate/normalize the expression of aromatase, lowering the conversion of androgens to estrogens.

But I agree.  You have to get their insulin down with a low glycemic index diet, maybe some intermittent fasting, and losing processed foods from the diet.  In order to get the most bang for the insulin buck, each insulin molecule needs to co-ordinate with 4 chromium ions, so if chromium intake is low (eating sugar is a great way to deplete chromium!) your insulin signaling is impaired.  Chromium polynicotinate with each meal can help with that.