My Quora Answer to:
If a psychosomatic disorder is a false argument, an argumentum ad ignorantiam (we can't find what you have, therefore you don't have anything), why do doctors still use it as a diagnosis?
Not being able to find the cause of somatic (non-psychiatric) symptoms is only one part of making the diagnosis of Somatic Symptom Disorder. This is from the Mayo Clinic site:
“Criteria for diagnosis
The Diagnostic and Statistical Manual of Mental Disorders (DSM-5), published by the American Psychiatric Association, emphasizes these points in the diagnosis of somatic symptom disorder:
You have one or more somatic symptoms — for example, pain or fatigue — that are distressing or cause problems in your daily life.
You have excessive and persistent thoughts about the seriousness of your symptoms, you have a persistently high level of anxiety about your health or symptoms, or you devote too much time and energy to your symptoms or health concerns.
You continue to have symptoms that concern you, typically for more than six months, even though the symptoms may vary.”
To answer your Question: a correct diagnosis leads to the proper therapy.