Current diagnostic models in medical practice do not adequately account for patient symptoms that cannot be classified. Standard medical practice involves ordering diagnostic tests based on a range of possibilities within a reasonable index of suspicion to classify symptoms within a disease-based framework. This leads experienced physicians to use a ‘hypothetico-deductive reasoning’ approach in order to make diagnoses, which involves arriving at an initial presumptive diagnosis and then asking questions to strengthen or disprove the tentative diagnosis, in conjunction with the patient history. This is the usual precursor to treatment. When common diagnoses are exhausted, physicians will turn to investigating less common possibilities and at the moment of perceived saturation where all known diagnostic possibilities have been excluded, physicians confront uncertainty in diagnosis

Diagnostic uncertainty in a clinical encounter is a common occurrence. Though the training that physicians receive engenders a certain intolerance of uncertainty and ambiguity. It has been suggested that in 25% to 50% of primary care visits no somatic cause is found to explain the patient’s presenting symptoms. This creates tension within a disease-based framework where treatment is based on identification of a cluster of symptoms which “reproduce, simplify and give a subjective content to the object they are supposed to stand for…” (1355).

The experience of illness in the absence of medical certainty can be extremely difficult and is often confounded in patients suffering from rare diseases. Qualitative research shows the confluence of themes between those of having a rare disease and those who present with MUPS (Medically Unexplained Physical Symptoms) such as a sense of guilt over being ill, a sense of chaos as a result of having consulted so many physicians and received so many contradictory examinations  and a fear that a diagnosis will never be reached.  There is also a powerful desire for legitimization, with the naming of the illness often showing itself to be more cathartic for the patient with MUPS or a rare disease than the condition necessarily being cured.