When making a diagnosis of somatic symptom disorder, what differentiates it from conversion disorder?

Conversion disorder requires certainty that symptoms are consciously feigned

Patients with somatic symptom disorder are preoccupied with having or acquiring a serious illness

In somatic symptom disorder, patients have disproportionate and persistent thoughts about the seriousness of their symptoms

In conversion disorder, patients must display la belle indifference (lack of concern about the nature or implications of the symptoms)