Actually, it's very important to get the correct diagnosis. RRMS and PPMS are very different, and while RRMS has many drugs available to treat it, PPMS currently has none.

RRMS (relapsing remitting multiple sclerosis) is identified by distinct relapses and remissions in disease activity. In other words, there will be periods where the patient's symptoms get dramatically worse, and then some weeks or months later the symptoms will go into remission, and the patient returns to their baseline state, perhaps with some residual effects left over from the relapse.

PPMS (primary progressive multiple sclerosis) patients never, ever experienced a remission. Their symptoms gradually worsen over time, the progression possibly plateauing for a while, but never backtracking as in a remission.

The other posters on this thread are correct, doctors are hesitant to label a patient with PPMS because insurance companies won't pay for treatments not specifically approved for a disease, and there currently aren't any for PPMS.

Many neurologist will try the RRMS drugs on their PPMS patients in hopes of slowing down the disease. It's better than doing nothing...