Actually, the difficulty of diagnosing PCOS varies according to the clinical presentation. In some cases, only one or two of the three above-mentioned components are present (e.g., ‘ovulatory PCOS’ or ‘non-hirsute anovulatory PCOS’ or ‘lean PCOS’ without hyperinsulinism). In practice, hyperandrogenic PCOS can be schematically split into classic and non-classic forms.

The Classic PCOS
In this situation, the clinical symptoms provide the most powerful presumption and their association in the three components has a very strong diagnostic potency, as well as their occurrence in the late stage of puberty. In this situation, the diagnostic use of ultrasonography is optional. The main difficulty is to avoid the pitfall of the ‘too much evident’ PCOS in adolescents referred either for hyperandrogenism or menstrual disorders. Therefore, it is still wise to check the basal serum T, DHEAS, 17-HP and prolactin (PRL) levels, as well as the urinary-free cortisol level, when obesity is recent and some Cushing syndrome stigmata are present.

The Non-Classic PCOS
PCOS remains the most likely explanation for a so-called idiopathic hirsutism (i.e., with ovulatory menstrual cycles). However, the clinical picture is not reliable enough in the absence of the other PCOS clinical components.

Therefore, one should rely on a cost-effective and safe work-up, which includes hormonal assays (see above) and ultrasonography. However, the finding of PCO at ultrasonography must not preclude other diagnosis since it may be incidentally associated with other conditions (in particular NCAH, see other diagnosis).