Misdiagnosis generally involves diagnosis and treatment of
a. symptoms and underlying cause of disease
b. a disease which patient actually suffers
c. a disease that the patient does not have
d. both a disease from which the patient actually suffers as well as symptoms and underlying causes of said disease

The answer is:  [C]:  "a disease that the patient does not have" .

Note:

Choice [A]:  "symptoms and underlying cause of disease" ;  this could be true in the case of "misdiagnosis". Since some delayed-onset diseases/medical conditions manifest that cannot be predicted and that do not occur unit many, many years later; misdiagnosis could be the interpretation of something else —or a provisional; diagnosis; or some working diagnosis/es; or diagnosis/es of symptoms.  However, this would NOT be consistent with what 'misdiagnosis' GENERALLY involves.

Choice:  [B]:  "a disease which patient actually suffers." 
       → incorrect answer choice.  This is NOT misdiagnosis but rather the correct, or proper, diagnosis.

Choice:  [C]:  "a disease that the patient does not have." ;
       → Yes; such a diagnosis and treatment of this is VERY consistent with "misdiagnosis".  This could definitely be a correct answer choice.

Choice:  [D]:  "both a disease from which the patient actually suffers as well as symptoms and underlying causes of said disease." ;
       → Incorrect response.  This answer choice provides:  1)  the incorrect, inconsistent response shown in "Choice [B]" ; along with:  2)  an incorrect response that is COMPLETELY opposite from and inconsistent with "misdiagnosis" (and supports the aforementioned "response # 1" mentioned in this very answer choice).

          The best answer choice — and correct answer choice — is:

   Answer choice:  [C]:  " a disease that the patient does not have" .