Medical assessment of patients with factitious disorder is analogous to piloting an airplane through dense clouds. In such flying conditions, pilots may feel panicky and disoriented. Their best response is to follow the basic rules of flying and trust their navigational instruments; pilots who depart from these procedures and rely instead on their own inner sense of direction and orientation are at risk for bad—even disastrous—outcomes.
Similarly, physicians encountering patients whom they cannot diagnose and who do not respond to the usual treatments may experience a feeling of panic and disorientation. When this occurs, their response should include the following:
Follow the basic procedures for responding to the patient’s signs and symptoms
Trust the reliability and validity of the medical tests that are performed
Respect base-rate information about the prevalence of various diseases that must be excluded
Cases abound in which tests have been repeated needlessly, invasive procedures performed without adequate justification, or medications prescribed with such apparent zeal that iatrogenic problems actually come to dominate the clinical picture.
Patients with factitious disorder use several techniques to disrupt the physician’s usual practices. Typically, they exploit the clinician’s fear of overlooking a rare life-threatening disease while also playing to his or her fascination with thorny medical problems; they well understand the appeal of a medical mystery and the personal satisfaction, notoriety, and esteem that come from solving one. In so doing, these patients encourage the physician to depart from standard procedures and to overlook more benign (and likely) explanations.
Paradoxically, patients with factitious disorder can also disrupt the physician’s usual practices by persuading him or her to forgo basic diagnostic procedures. Striking evidence of this phenomenon is noted in reports of patients who have successfully feigned diseases such as AIDS with Kaposi sarcoma and malignancies such as breast cancer. In both of these real-life examples, definitive tests were available to establish the presence of these diseases, but they were not performed.
One reason for the failure to perform definitive tests in situations such as these is that the patients’ persuasive but false medical history, perhaps combined with their physical appearance, may lead to the mistaken assumption that the tests are unnecessary. Another is that doctors may erroneously believe that such serious and life-threatening illnesses cannot possibly be feigned or self-induced.
Any testing ordered should be based on a well-considered and appropriately prioritized differential diagnosis. The performance of any procedures should be approached very conservatively if suspicions of factitious disorder are raised (eg, if the patient has the “roadmap” abdomen caused by scars from prior exploratory operations). Tests should not be needlessly repeated in the misguided hope that the pathology will suddenly emerge.
Laboratory studies can be especially helpful in facilitating the diagnosis of many physical illnesses as factitious.
For example, patients with hypoglycemia can be assessed for exogenous insulin injection by determining the serum insulin−to−C-peptide ratio during a hypoglycemic episode.  Patients who complain of kidney stones can be asked to filter their urine for stones, and the submitted material can be tested for composition. A tissue biopsy can be helpful in revealing the factitious nature of lesions in which foreign material has been injected to simulate naturally occurring disease.
A common finding in factitious disorder is test results that are inconsistent with the claimed illness (eg, no elevated white blood cell [WBC] count or left shift in apparent sepsis or necrotizing fasciitis). Bacterial cultures may grow an overly wide variety of enteric flora when taken from infected sites distant from the pelvis or groin because the patient has contaminated the wound with feces. Self-induced Intractable diarrhea or vomiting may be missed unless the laboratory personnel are specifically asked to look for agents such as phenolphthalein or ipecac.
Because the range of factitious illnesses is limited only by the imagination of the perpetrator, it would be impossible to list all of the laboratory tests that might prove useful in one circumstance or another. However, suspicion that an illness is factitious should be conveyed to the pathologist, who may be able to help identify ways of confirming the diagnosis. 
A particular difficulty with laboratory testing in patients with factitious disorder is that many of these patients have a medical background and thus are likely to be familiar with the routine tests performed for a particular presentation. For example, a patient with anemia could anticipate that routine blood work would not include screens for the anticoagulants he or she has ingested and that the medical or surgical investigation would consequently be prolonged as the professionals search for the elusive etiology (eg, unexplained hematuria or hematochezia).
The number of other ways in which patients have used tests and test results to mislead doctors is staggering. For example, some individuals self-inject insulin to create a baffling, tenacious, and dangerous hypoglycemic state. As noted (see above), this ruse can be exposed before an erroneous diagnosis of insulinoma is made by assessing whether the C-peptide level is compatible with the serum insulin level. A high insulin level combined with a low C-peptide level indicates factitious hypoglycemia.
As further examples, some patients create alarming laboratory evidence of proteinuria simply by adding a drop of egg white (a pure protein) to their urine specimens. In others, a small amount of blood, perhaps added to a stool specimen or swallowed before endoscopy, appears as conclusive evidence of gastrointestinal pathology. The presence of unexplained puncture sites, especially in odd areas (eg, the base of the tongue) can provide very compelling evidence of such dissimulation.
Some patients enter the nurses’ station or access the clipboards outside their doors and directly change laboratory values from normal to abnormal. Often, they present the doctor with letters from colleagues purporting to verify the pathology, but a follow-up call reveals that the letterhead paper was stolen and the report was typed by the patient. Of course, illnesses that are self-induced but real (eg, extreme lead poisoning from drinking water in which lead-based items were boiled) show corresponding authentic analyses that mandate emergency treatment.
As with laboratory testing, almost any imaging technique is at least potentially useful in the workup of a patient with suspected factitious disorder.
Imaging may be particularly useful when the patient presents with a well-established medical problem of the type that can be easily imaged (eg, inoperable malignancies or cardiovascular accidents). In such cases, errors are made by eschewing these tests to spare the patient the expense or inconvenience of repeating tests that have already returned positive indications of disease. For many patients with factitious disorder, the use of imaging studies becomes part of the search for an explanation for their puzzling signs and symptoms.
Strongly subjective tests, such as electromyography and nerve conduction velocity tests, should be understood as almost never definitive in isolation. An occasional positive finding, which is likely whenever anyone is subjected to extremely extensive and repeated testing, should not be misinterpreted. Clinicians should remember that each intervention poses a risk of iatrogenic complications that only complicate the picture. Indeed, such complications have led to malpractice actions against physicians.
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