Other Specified or Unspecified Bipolar and Related Disorders
(formerly Bipolar Disorder NOS)

Article written and reviewed by Dr Luca Moretti

The categories other specified bipolar and related disorder and unspecified bipolar and related disorder are used in the DSM-5-TR when manifestations characteristic of the bipolar spectrum predominate and cause clinically significant distress or functional impairment, but all requirements for bipolar I disorder, bipolar II disorder, cyclothymic disorder or another defined bipolar category are not met.

These diagnoses replaced part of the broad DSM-IV category of bipolar disorder not otherwise specified, often abbreviated as bipolar disorder NOS. The new distinction increases precision: in the other specified category, the clinician explicitly states why criteria for a more defined bipolar disorder are not met; in the unspecified category, the reason is not stated, for example because information is insufficient or the context does not allow a complete diagnostic assessment.

This is not a single form of illness with its own biological course. The categories include heterogeneous presentations united by the clinical relevance of subthreshold or incompletely characterized bipolar symptoms. The diagnosis therefore does not justify assuming that all patients have the same prognosis, the same risk of progression or the same pharmacological response.

ICD-11 includes conceptually similar categories, including other specified bipolar or related disorders, code 6A6Y, and bipolar or related disorders, unspecified, code 6A6Z. Correspondence between DSM-5-TR and ICD-11 is not necessarily one to one, and coding should follow the classification system actually being used.

There is no single contemporary and directly comparable epidemiological prevalence for these categories. Historical estimates of the so called subthreshold bipolar spectrum depend heavily on the criteria used; in the World Mental Health Survey Initiative, subthreshold bipolar presentations were more common than bipolar I or II disorder considered separately, but these data do not automatically equal the prevalence of the current DSM-5-TR other specified or unspecified categories.

The main clinical relevance is to recognize a presentation that should neither be ignored nor forced into a more specific diagnosis without sufficient evidence. A brief period of euphoria, irritability, emotional instability or reduced sleep does not automatically represent bipolarity. Change from usual functioning, syndromic constellation, duration, episodic course and differential diagnosis are required.

Etiology, Pathogenesis and Pathophysiology

Residual bipolar categories do not have a demonstrated independent etiology. Because they include different phenotypes, it would be inappropriate to attribute a specific neurochemical, genetic or anatomical alteration to them. Biological mechanisms are interpreted in light of knowledge about bipolar disorders as a whole and the patient’s specific presentation.

A family history of bipolar disorder increases the probability that subthreshold affective symptoms belong to a bipolar spectrum but is not diagnostic. Bipolar disorder has a strong polygenic component, with hundreds of associated loci identified by genome wide studies; however, no genetic score can classify an individual with incomplete symptoms as bipolar.

Genetic overlap with schizophrenia, major depression and other psychiatric phenotypes shows that biological boundaries do not perfectly coincide with diagnostic ones. This overlap makes it even more important to avoid inferences such as “family history equals diagnosis” and to base classification on the documented clinical course.

Dopaminergic, glutamatergic, serotonergic and noradrenergic neurotransmission, synaptic plasticity, mitochondrial function and intracellular pathways have been implicated in the pathophysiology of bipolar disorders. These associations, however, derive mainly from studies of bipolar I or II disorder and do not define a mechanism specific to other specified or unspecified categories.

Regulation of sleep and circadian rhythms may be particularly informative. Reduced need for sleep associated with increased energy has greater bipolar significance than simple insomnia with fatigue. Shift work, sleep deprivation and circadian irregularity may precipitate symptoms in vulnerable individuals but are not by themselves evidence of bipolar illness.

Stressful events, early trauma, relational conflict and changes in routines may precede mood fluctuations. These factors act as risk modifiers, not sufficient causes. Immediate affective reactivity to interpersonal events, for example, may also point toward different diagnoses and should be analyzed within the context of the entire temporal pattern.

Medications and substances are particularly important etiologic considerations in the differential diagnosis. Stimulants, corticosteroids and other exposures may produce activation, insomnia or manic syndromes; recreational substances may mimic or precipitate bipolar symptoms. When there is an etiologic relationship with the exposure, classification may fall under substance or medication induced bipolar and related disorder rather than a primary residual category.

Neurological and endocrine conditions may also produce similar symptoms. Late onset, sudden personality change, neurological signs or an atypical course increase the need to investigate an underlying medical condition. If the mood disorder is a direct pathophysiological consequence of the medical condition, the diagnosis should reflect that relationship.

Neuroimaging and electrophysiological studies have identified average differences in prefrontal and limbic circuits in bipolar disorders, but overlap between patients and controls is substantial. No magnetic resonance imaging or EEG pattern distinguishes a patient with a subthreshold bipolar presentation from a person without the disorder.

Residual categories may include people at different diagnostic stages: some maintain a subthreshold presentation over time, others are later reclassified when full episodes emerge, and still others receive a different diagnosis after a more complete history is obtained. This heterogeneity should not be interpreted as an obligatory sequence of progression toward bipolar I or II disorder.

The concept of a bipolar spectrum is useful in research and clinical formulation but does not justify indiscriminately lowering diagnostic thresholds. Excessive extension of the concept risks classifying normal temperamental variation, ADHD, personality disorders, substance effects or other conditions as bipolar.

In the absence of validated biomarkers, pathophysiology cannot be used to resolve diagnostic uncertainty. The operational criterion remains longitudinal phenomenology: the quality of mood disturbance, increase in energy and activity, associated symptoms, duration, periodicity, impairment and alternative causes.

Clinical Manifestations

Clinical manifestations are by definition heterogeneous. A patient may have major depressive episodes accompanied by periods of activation that are too brief or contain too few symptoms to meet full hypomania criteria, or may show cyclothymic patterns of shorter duration than the required threshold.

The DSM-5-TR describes several example presentations within the other specified category. These examples do not exhaust all possible cases and must be applied together with the general requirements of clinical significance and exclusion of alternative diagnoses.

• Short-duration hypomanic-like episodes (short-duration hypomanic-like episodes), lasting 2 to 3 days, associated with one or more major depressive episodes.
• Hypomanic-like episodes with insufficient symptoms (hypomanic-like episodes with insufficient symptoms) associated with one or more major depressive episodes.
• Hypomanic episodes without a previous major depressive episode when the presentation does not meet requirements for another bipolar category.
• Cyclothymic presentation of insufficient duration (cyclothymic-like disorder), when the characteristic pattern is present for less than the duration required for cyclothymic disorder.

In presentations with short-duration hypomanic-like episodes, the quality of symptoms must be convincing: increased energy and activity, reduced need for sleep, greater talkativeness, racing thoughts, grandiosity, distractibility or impulsive behavior must represent a clear change from baseline. Insomnia alone or a single day of good mood is not sufficient.

When the issue is an insufficient number of symptoms, duration may be compatible with hypomania but the syndromic constellation does not reach the full threshold. This presentation should be distinguished from hyperthymic temperament, personality traits, stimulant use and physiological variations in energy.

The possible presence of a hypomanic episode without a history of major depression requires particular caution. An isolated hypomanic episode does not meet criteria for bipolar II disorder and is not equivalent to mania. Follow up may clarify the course, but it is not possible to predict with certainty whether a major depressive episode will occur in the future.

A cyclothymic presentation of insufficient duration includes numerous periods of hypomanic and depressive symptoms resembling cyclothymic disorder but not meeting the required time threshold. It is essential to distinguish a persistent affective pattern from transient, context dependent fluctuations.

The unspecified category may be used when symptoms are clearly compatible with the bipolar domain and clinically significant, but the clinician does not have enough information to state why criteria for a more precise diagnosis are not met. Emergency settings or incomplete initial assessments are typical examples, but the category is not limited to them.

The patient may present during depression, making periods of activation the main historical feature to investigate. Brief episodes may easily be forgotten or remembered positively; reconstruction with close contacts, when appropriate, may improve accuracy.

Sleep is particularly useful in characterization. During hypomania, the patient sleeps less without feeling tired and continues to have energy; in anxiety related or depressive insomnia, by contrast, reduced sleep is generally accompanied by fatigue and a desire to sleep. This distinction is not absolute but contributes to clinical formulation.

Impulsive behavior, spending, risky sexual activity, increased project initiation, irritability and conflict should be investigated. Even when the threshold for a full episode is not met, these manifestations may cause clinically significant consequences.

The presence of psychosis during a period of elevated mood substantially changes classification: in the DSM, psychosis makes the episode manic if the other requirements are met and therefore points toward bipolar I disorder rather than subthreshold hypomania.

Anxiety comorbidities, ADHD, substance use disorders and personality disorders are common in populations with affective symptoms and may produce phenomenological overlap. A residual diagnosis should not become a container for every form of emotional instability.

Assessment of suicide risk is necessary regardless of whether the patient meets criteria for a full bipolar diagnosis. Depression, mixed features, agitation, substance use and previous attempts may also occur in subthreshold presentations.

Assessment and Diagnosis

Diagnosis first requires demonstrating that symptoms belong to the bipolar domain and are clinically significant. Observing mood fluctuations is not enough. Distinct episodes, changes in energy and activity, sleep, associated symptoms, duration, functioning and the relationship with substances or medical conditions must be reconstructed.

The next step is to systematically determine whether criteria for bipolar I disorder, bipolar II disorder or cyclothymic disorder are met. A residual category is used only after establishing that a more specific diagnosis does not adequately describe the presentation.

For the other specified category, the clinician must record the reason why the presentation does not meet full requirements. The reason becomes part of the diagnostic formulation, as in short duration hypomania like episodes or cyclothymia like presentations of insufficient duration. There is therefore no single independent list of symptom criteria equivalent to that for mania or hypomania.

In the unspecified category, by contrast, the reason is not stated. This may be due to insufficient information, inability to obtain a reliable history or a clinical decision not to specify further at that stage. The diagnosis should be reassessed when new data become available.

The longitudinal history should investigate previous major depressions, duration and intensity of activation periods, hospitalizations, psychosis, family history and treatment response. It is useful to ask specifically about reduced need for sleep and increased activity because a generic question about euphoria has limited sensitivity.

Information from family members or people living with the patient may be particularly useful when insight during activation was reduced. This material should not replace the interview with the patient but may clarify whether the change was observable and unequivocal.

Screening scales such as the Mood Disorder Questionnaire may suggest the need for further assessment but do not establish a diagnosis. A positive score may occur in other conditions and cannot determine whether the presentation is bipolar I, bipolar II, cyclothymic or residual.

Differential diagnosis includes unipolar depression, ADHD, borderline personality disorder, anxiety disorders, psychotic disorders and substance related disorders. The episodic and autonomous nature of changes, increased energy and reduced need for sleep are particularly important features, but none should be interpreted in isolation.

Substances and medications should be assessed in temporal relation to symptoms. Stimulants, corticosteroids and other exposures may produce activation; if the presentation is attributable to these effects, a substance or medication induced diagnosis should be considered rather than a primary residual category.

Medical investigations are guided by history and examination. TSH, complete blood count, electrolytes, renal and liver function, toxicology tests and other investigations may be appropriate depending on the case. There is no laboratory test that confirms the diagnosis.

Neuroimaging or EEG is requested only when neurological signs, atypical onset, seizures, confusion or other features suggest possible brain disease. Magnetic resonance imaging does not identify a diagnostic signature of subthreshold bipolarity.

Follow up is part of the diagnostic assessment. The emergence of a manic episode, a full hypomanic episode or a sufficiently prolonged cyclothymic pattern may allow reclassification; conversely, additional information may point toward a nonbipolar disorder. A residual diagnosis should not be regarded as necessarily definitive or necessarily temporary.

Treatment and Prognosis

There is no pharmacological treatment validated specifically for the labels other specified or unspecified independently of the clinical presentation. Treatment studies in bipolar disorders mainly enroll patients with bipolar I or II disorder and do not support automatically transferring the same treatment hierarchies to all subthreshold presentations.

The first principle is to treat the syndrome actually present and immediate risk. A patient with clinically significant depression, agitation, insomnia or suicidal behavior needs interventions directed at those problems while maintaining appropriate caution regarding possible bipolarity.

When a presentation has strongly bipolar features, medication choice may be guided by evidence from major bipolar disorders, but should be individualized and preferably specialist led. The mere presence of a residual diagnosis does not automatically justify the use of lithium, valproate or antipsychotics.

Antidepressants require caution when there is substantial suspicion of bipolarity, especially in the presence of mixed features, previous activation or a suggestive family history. Antidepressant monotherapy should not be used as an automatic diagnostic and therapeutic response in a patient whose polarity has not been adequately assessed.

Psychoeducation, regular sleep, recognition of early warning signs and reduction of substance use may be useful regardless of pharmacological treatment. Psychotherapies used in bipolar disorders, including cognitive, family based and social rhythm focused strategies, may be considered according to the patient’s needs.

When pharmacological treatment is started, the same safety monitoring standards required for the medication used must be followed: renal and thyroid function for lithium, metabolic parameters for many antipsychotics, reproductive risk assessment for teratogenic medications and monitoring of interactions.

Follow up should document the duration and frequency of fluctuations, sleep, functioning, depressive symptoms, any manic signs and treatment response. A mood diary may be useful in supporting reconstruction, although it does not replace clinical assessment.

Prognosis cannot be described as inevitable progression to bipolar I or II disorder. Some patients later develop full episodes and are reclassified; others maintain a subthreshold presentation; in still others, an alternative diagnosis becomes more appropriate. Prognostic meaning depends on the specific phenotype.

A family history of bipolar disorder, early onset, convincing hypomanic symptoms, recurrent depressive episodes and mixed features may increase suspicion of a bipolar course but cannot predict an individual patient’s trajectory with certainty.

The goal is to avoid two opposite errors: underdiagnosing clinically significant bipolarity and overdiagnosing every form of emotional instability as bipolar. Accurate longitudinal reassessment is often more useful than immediately forcing the presentation into a more specific category.

Complications

Complications depend on the presentation and may include those seen in more clearly defined bipolar disorders, especially when significant depression, mixed features or impulsivity are present. Suicide risk should be assessed directly and cannot be considered negligible simply because full bipolar criteria are not met.

Periods of activation may lead to spending, conflict, risky sexual behavior and impulsive decisions even when duration or symptom count is subthreshold. The extent of functional consequences contributes to establishing the clinical significance of the presentation.

Recurrent depression may cause isolation, reduced productivity, job loss and deterioration in quality of life. Diagnostic uncertainty does not reduce the actual burden of symptoms and should not delay necessary interventions.

Alcohol or other substance use may worsen instability, impulsivity, sleep and suicide risk and make it more difficult to distinguish spontaneous episodes from induced symptoms. Substance management is therefore an integral part of follow up.

One possible clinical complication is inappropriate treatment resulting from an incomplete diagnosis. Attributing underlying bipolar depression to unipolar depression, or diagnosing bipolarity when another disorder is present, may expose the patient to less effective strategies or avoidable adverse effects.

Fragmented care may prevent recognition of the course: brief episodes documented by different professionals may not be linked together. A shared longitudinal history improves the ability to identify recurring patterns.

When the presentation is subsequently reclassified as bipolar I, bipolar II or cyclothymic disorder, this does not necessarily represent a “worsening” caused by the previous diagnosis; it may reflect the natural progressive availability of diagnostic information over time.

Preventing complications therefore requires monitoring mood, sleep, suicidality, substance use, functioning and treatment response, while remaining open to revising the diagnosis without turning uncertainty into clinical inertia.

Bibliography
1. American Psychiatric Association. Diagnostic and Statistical Manual of Mental Disorders, Fifth Edition, Text Revision (DSM-5-TR). American Psychiatric Association Publishing; 2022.
2. World Health Organization. Clinical descriptions and diagnostic requirements for ICD-11 mental, behavioural and neurodevelopmental disorders. World Health Organization; 2024.
3. American Psychiatric Association. DSM-5-TR Update, September 2025. American Psychiatric Association; 2025.
4. Yatham LN et al. Canadian Network for Mood and Anxiety Treatments and International Society for Bipolar Disorders 2018 guidelines for the management of patients with bipolar disorder. Bipolar Disorders. 20(2), 2018: 97-170.
5. Keramatian K et al. The CANMAT and ISBD Guidelines for the Treatment of Bipolar Disorder: Summary and a 2023 Update of Evidence. Focus. 21(4), 2023: 344-353.
6. Department of Veterans Affairs et al. VA/DoD Clinical Practice Guideline for Management of Bipolar Disorder. Version 2.0. Department of Veterans Affairs and Department of Defense; 2023.
7. National Institute for Health and Care Excellence. Bipolar disorder: assessment and management. Clinical Guideline CG185. National Institute for Health and Care Excellence; updated 2025.
8. Singh B et al. Bipolar disorder. The Lancet. 406(10506), 2025: 963-978.
9. McIntyre RS et al. Bipolar disorders. The Lancet. 396(10265), 2020: 1841-1856.
10. McIntyre RS et al. The clinical characterization of the adult patient with bipolar disorder aimed at personalization of management. World Psychiatry. 21(3), 2022: 364-387.
11. O’Connell KS et al. Genomics yields biological and phenotypic insights into bipolar disorder. Nature. 639(8056), 2025: 968-975.
12. Mullins N et al. Genome-wide association study of more than 40,000 bipolar disorder cases provides new insights into the underlying biology. Nature Genetics. 53(6), 2021: 817-829.
13. Merikangas KR et al. Prevalence and correlates of bipolar spectrum disorder in the World Mental Health Survey Initiative. Archives of General Psychiatry. 68(3), 2011: 241-251.
14. Nusslock R et al. Subthreshold bipolarity: diagnostic issues and challenges. Bipolar Disorders. 13(7-8), 2011: 587-603.
15. Angst J. Bipolar disorders in DSM-5: strengths, problems and perspectives. International Journal of Bipolar Disorders. 1, 2013: 12.