Differences in phenomenology, family history, longitudinal course, and responses to treatment suggest that this is not the case. Researchers have found "only a modest association" between bipolar disorder and borderline personality disorder, with "a strong spectrum relationship with [BPD and] bipolar disorder extremely unlikely". Benazzi et al. suggest that the DSM-IV BPD diagnosis combines two unrelated characteristics: an affective instability dimension related to bipolar II and an impulsivity dimension not related to bipolar II. Premenstrual dysphoric disorder
Premenstrual dysphoric disorder (PMDD) occurs in 3–8% of women. Symptoms begin during the luteal phase of the menstrual cycle, and end during menstruation. Symptoms may include marked mood swings, irritability, depressed mood, feeling hopeless or suicidal, a subjective sense of being overwhelmed or out of control, anxiety, binge eating, difficulty concentrating, and substantial impairment of interpersonal relationships. People with PMDD typically begin to experience symptoms in their early twenties, although many do not seek treatment until their early thirties.Although some of the symptoms of PMDD and BPD are similar, they are different disorders. They are distinguishable by the timing and duration of symptoms, which are markedly different: the symptoms of PMDD occur only during the luteal phase of the menstrual cycle, whereas BPD symptoms occur persistently at all stages of the menstrual cycle. In addition, the symptoms of PMDD do not include impulsivity. Comorbid Axis II disorders
About three-fourths of people diagnosed with BPD also meet the criteria for another Axis II personality disorder at some point in their lives. (In a major 2008 study—see adjacent table—the rate was 73.9%.)
Other causes that may lead to similar symptoms include ischemic kidney failure (kidney dysfunction due to an interrupted blood supply), a group of diseases known as thrombotic microangiopathies and endocarditis (infection of the heart valves with small clumps of infected tissue embolizing through the body). Blood and urine
Tests for inflammation (C-reactive protein and the erythrocyte sedimentation rate) are typically elevated, and abnormal liver enzymes may be seen. If the kidneys are involved, tests of kidney function (such as urea and creatinine) are elevated. The complete blood count may show particularly high numbers of a type of white blood cell known as eosinophils (more than 0.5 billion per liter); this occurs in only 60-80% of cases, so normal eosinophil counts do not rule out the diagnosis. Examination of the urine may show red blood cells (occasionally in casts as seen under the microscope) and increased levels of protein; in a third of the cases with kidney involvement, eosinophils can also be detected in the urine. If vasculitis is suspected, complement levels may be determined as reduced levels are often encountered in vasculitis; complement is a group of proteins that forms part of the innate immune system. Complement levels are frequently reduced in cholesterol embolism, limiting the use of this test in the distinction between vasculitis and cholesterol embolism. Tissue diagnosis
The microscopic examination of tissue (histology) gives the definitive diagnosis. The diagnostic histopathologic finding is intravascular cholesterol crystals, which are seen as cholesterol clefts in routinely processed tissue (embedded in paraffin wax).