The red blood cell/plasma lithium ratio: marker of biological heterogeneity within bipolar affective illness?

Lithium in the treatment of bipolar disorder: pharmacology and pharmacogenetics

After decades of research, the mechanism of action of lithium in preventing recurrences of bipolar disorder remains only partially understood. Lithium research is complicated by the absence of suitable animal models of bipolar disorder and by having to rely on in vitro studies of peripheral tissues. A number of distinct hypotheses emerged over the years, but none has been conclusively supported or rejected. The common theme emerging from pharmacological and genetic studies is that lithium affects multiple steps in cellular signaling, usually enhancing basal and inhibiting stimulated activities. Some of the key nodes of these regulatory networks include GSK3 (glycogen synthase kinase 3), CREB (cAMP response element-binding protein) and Na(+)-K(+) ATPase. Genetic and pharmacogenetic studies are starting to generate promising findings, but remain limited by small sample sizes. As full responders to lithium seem to represent a unique clinical population, there is inherent value and need for studies of lithium responders. Such studies will be an opportunity to uncover specific effects of lithium in those individuals who clearly benefit from the treatment.

Profiles of "manic" symptoms in bipolar I, bipolar II and major depressive disorders

BACKGROUND

Classical authors such as Kraepelin, as well as the emerging literature during the past decade, indicate that manic-like signs and symptoms are present to a variable degree in all mood disorders. Current nosography does not differentiate between them and only the number of symptoms or severity is used for classification. This is particularly true for mania and hypomania. This paper will analyze the patterns of manic symptoms in bipolar I (BP-I), bipolar II (BP-II) and major depressive disorders (MDD), to test the hypothesis that mania and hypomania have different profiles, and ascertain which excitatory manic phenomena do occur in unipolar MDD.

METHODS

Six hundred and fifty-two inpatients (158 BP-I, 122 BP-II and 372 MDD) were assessed using the operational criteria for psychotic illness checklist (OPCRIT) [Arch. Gen. Psychiatry 48 (1991) 764] with a lifetime perspective. Manic or hypomanic symptoms were investigated and compared between BP-I, BP-II and MDD.

RESULTS

When compared with BP-II, BP-I disorder had a higher prevalence of reckless activity, distractibility, psychomotor agitation, irritable mood and increased self-esteem. These five symptoms correctly classified 82.8% of BP-I and 80.1% of BP-II patients. One or two manic symptoms were observed in more than 30% of major depressive patients; psychomotor agitation was the most frequent manifestations present in 18% of the MDD group.

LIMITATIONS

We did not control for severity of symptoms, nor for neuroleptic use that could produce akathisia.

CONCLUSIONS

This study suggests that mania and hypomania can be differentiated in their symptom profiles, and highlights the presence of few manic symptoms, particularly psychomotor agitation, in MDD. From the standpoint of number of manic signs and symptoms, controlling for psychomotor agitation did not substantially change the predictive power of the remaining manic symptoms. Given that excitatory manic signs and symptoms are present to a decreasing degree in BP-I, BP-II and MDD, these disorders can be proposed to lie along a dimensional model. Overall, these data are compatible with the concept of a bipolar spectrum, whereby each of the affective subtypes requires specific genetic factors.

The comparative clinical phenotype and long term longitudinal episode course of bipolar I and II: a clinical spectrum or distinct disorders?

BACKGROUND

The present analyses were designed to compare the clinical characteristics and long-term episode course of Bipolar-I and Bipolar-II patients in order to help clarify the relationship between these disorders and to test the bipolar spectrum hypothesis.

METHODS

The patient sample consisted of 135 definite RDC Bipolar-I (BP-I) and 71 definite RDC Bipolar-II patients who entered the NIMH Collaborative Depression Study (CDS) between 1978 and 1981; and were followed systematically for up to 20 years. Groups were compared on demographic and clinical characteristics at intake, and lifetime comorbidity of anxiety and substance use disorders. Subsets of patients were compared on the number and type of affective episodes and the duration of inter-episode well intervals observed during a 10-year period following their resolution of the intake affective episode.

RESULTS

BP-I and BP-II had similar demographic characteristics and ages of onset of their first affective episode. Both disorders had more lifetime comorbid substance abuse disorders than the general population. BP-II had a significantly higher lifetime prevalence of anxiety disorders in general, and social and simple phobias in particular, compared to BP-I. Intake episodes of BP-I were significantly more acutely severe. BP-II patietns had a substantially more chronic course, with significantly more major and minor depressive episodes and shorter inter-episode well intervals. BP-II patients were prescribed somatic treatment a substantially lower percentage of time during and between affective episodes.

LIMITATIONS

BP-I patients with severe manic course are less likely to be retained in long-term follow-up, whereas the reverse might be true for BP-II patients who are significantly more prone to depression (i.e., patients with less inclination to depression and with good prognosis may have dropped out in greater proportions); this could increase the gap in long term course characteristics between the two samples. The greater chronicity of BP-II may be due, in part, to the fact that the patients were prescribed somatic treatments substantially less often both during and between affective episodes.

CONCLUSIONS

The variety in severity of the affective episodes shows that bipolar disorders, similar to unipolar disorders, are expressed longitudinally during their course as a dimensional illness. The similarities of the clinical phenotypes of BP-I and BP-II, suggest that BP-I and BP-II are likely to exist in a disease spectrum. They are, however, sufficiently distinct in terms of long-term course (i.e., BP-I with more severe episodes, and BP-II more chronic with a predominantly depressive course), that they are best classified as two separate subtypes in the official classification systems.

Bipolar II disorder and suicidal behavior

Despite the fact that the nosologic position of bipolar II disorder continues to be debated, several lines of research indicate that it is a distinct nosologic category that should be separated from both bipolar I and unipolar major depression. This review of the authors' and others' work demonstrates that the lifetime risk of suicide attempts is highest in bipolar II and lowest in unipolar patients, whereas risk is intermediate in bipolar I patients. Moreover, two reports show that bipolar II patients are over represented among suicide victims. Clinicians must take great care in not missing this diagnosis, which, when untreated, has ominous prognostic implications.

Suicide in subtypes of primary major depression

Among 100 consecutive suicide victims with primary major depression at the time of their suicide, 46% were found to have had bipolar II depression, 1% bipolar I disorder and 53% non-bipolar major depression. Since the lifetime prevalence rates of bipolar II and bipolar I depressions are relatively low compared to primary major non-bipolar depression, the present findings suggest that bipolar II disorder gives a particularly high risk of suicide among the different subtypes of primary major affective illness. Fifty-nine percent of the patients had medical contact during the depressive episode, but the depression was frequently undiagnosed, untreated or undertreated. The implications of these findings for suicide prevention are discussed briefly.

Prophylaxis and the lithium ratio in bipolar patients

Thirty-five bipolar outpatients treated with lithium carbonate were followed for up to 5 years with the aim of studying the relation of the lithium ratio (LR) and its predictive value. Only male responders were found to have higher LR than male nonresponders. No difference was found between the mean LR of men and women, as a group. Aging also had no effect on LR. Positive family history of affective disorders was correlated with high LR, irrespective of response.

Lithium transport in red cells of patients with affective disorders

Variation in red cell Li+ transport as mediated by the Li+-Na+ exchange pathway (Li+-Na+ counterflow) appears to cause wide variation between psychiatric patients in the Li+ ratio (erythrocyte/plasma) in vivo during Li+ treatment. We obtained significant correlations between Li+ ratios determined in vivo and several measures of Li+ transport as mediated by Li+-Na+ exchange. Patients with bipolar illness had significantly lower rates of Li+ transport as mediated by this pathway than did normal subjects.

Classification and diagnosis of depression

There is no general consensus how to classify and diagnose depressive disorders. The main reason is disagreement regarding etiology. This is reflected in the several theoretical models of depression which has been proposed. On the other hand, a reliable way of characterizing groups of patients that can be used by both clinicians and researchers, is necessary both for communication and progress of research. Facing this situation, the inclusion of etiological theories in classification of depression obviously would be an obstacle to the use of such a classification system by clinicians of various theoretical orientation at current. Thus, a classification system which describes the clinical features of the mental disorders comprehensively and at the lowest order of inference necessary to identify the disorder in a reliable way is needed. The third edition of the Diagnostic and Statistical Manual of Mental Disorder (DSM-III) represents such a classification system. By providing operational diagnostic criteria for each diagnosis, DSM-III represents a major achievement of classification in clinical psychiatry and research. This paper will present the classification of depression and the problem of differential diagnosis as outlined in DSM-III. Further, the validity of the DSM-III classification of depression will be discussed with reference to some recent research findings on biopsychosocial and treatment aspects of depressive disorders.