Definition of an MDI:
What is a "Medically Determinable Impairment"?
A medically determinable physical or mental impairment is an impairment that results from anatomical, physiological, or psychological abnormalities that can be shown by medically acceptable clinical and laboratory diagnostic techniques. The medical evidence must establish that an individual has a physical or mental impairment; a statement about the individual's symptoms is not enough.https://www.ssa.gov/disability/professionals/bluebook/general-info.htmSee also:
DI 24501.020 Establishing a Medically Determinable Impairment (MDI)
A. DefinitionsFor the purposes of determining whether the claimant has a "medically determinable impairment (MDI)", the following definitions apply:
-Objective medical evidence means signs, laboratory findings, or both.
-Signs are one or more anatomical, physiological, or psychological abnormalities that are observable, apart from the claimant's statements (description of symptoms). Signs must be shown by medically acceptable clinical diagnostic techniques. Psychiatric signs are medically demonstrable phenomena that indicate specific psychological abnormalities, e.g., abnormalities of behavior, mood, thought, memory, orientation, development, or perception. Psychiatric signs must be shown by observable facts that can be medically described and evaluated.
-Laboratory findings are one or more anatomical, physiological, or psychological phenomena that can be shown by the use of medically acceptable laboratory diagnostic techniques. Diagnostic techniques include chemical tests (such as blood tests), electrophysiological studies (such as electrocardiograms and electroencephalograms), medical imaging (such as X-rays), and psychological tests.
NOTE: Symptoms are the claimant's own description of his or her physical or mental impairment(s). Symptoms cannot establish the existence of an MDI.
B. Establishing The Existence Of An MDIWe need objective medical evidence from an acceptable medical source (AMS) to establish the existence of an MDI. See DI 22505.003 Evidence from an Acceptable Medical Source (AMS).
We cannot establish a MDI using any other kind of evidence, including:
-A claimant's statement about his or her symptoms,
-A diagnosis, or
-A medical opinion.
C. Symptom EvaluationOnly after we establish the claimant has an MDI based on objective medical evidence from an AMS, can we then evaluate the extent to which symptoms may affect the claimant's ability to perform work-related activities for an adult or ability to function independently, appropriately, and effectively in an age-appropriate manner for a child under age 18.
If there is no MDI, or if the established MDI could not reasonably be expected to produce the claimant's symptoms, we will find those symptoms do not affect the ability to perform work-related activities for an adult or the ability to function independently, appropriately, and effectively in an age-appropriate manner for a child under age 18.
For a detailed discussion on how to evaluate symptoms, see Social Security Ruling 16-3p: Titles II and XVI: Evaluation of Symptoms in Disability Claims and DI 24501.021: Evaluating Symptoms.
https://secure.ssa.gov/poms.nsf/lnx/0424501020So I guess technically you don't have to have a diagnosis of an MDI; you just have to establish the existence of an MDI via "objective medical evidence" which is defined as "signs" and/or "laboratory findings" above (both signs and lab finding are also defined above).
You wrote, "no tests which can point to a specific deviation that would explain their illness and its symptoms." Well, they may not have a specific diagnosis, but are there absolutely no unusual lab findings and/or nothing abnormal that could be observed by an acceptable medical source to prove an MDI exists?
Usually establishing an MDI isn't the biggest hurdle in the 5-step sequential evaluation process. Yes. I would think it might be more difficult if your doctors can't agree what is going on with you medically and there's not a definitive diagnosis, but let's say you have terrible diarrhea every 10 minutes or something and are losing a lot of weight. Maybe the doctors haven't pinpointed the exact cause, but I assume one's doctor could document the number of trips made to the bathroom during each doctor's appointment and even check your stool once or twice and keep track of your weight loss over time. I'm just trying to brainstorm to give an example here. Maybe not the greatest example?