The association between multiple sclerosis (MS) and depression is well-established. Are people with MS also at risk of developing bipolar disorder?

Key points

• Bipolar disorder is significantly more common in people with MS than in the general population.
• This is not merely a byproduct of the stress of chronic illness; it also has to do with changes in the brain, caused by MS, that affect mood as well as physical function.
• Mood symptoms may be caused by MS lesions, disease-related inflammation, or medications (steroids in particular).
• Differentiating ‘primary’ (organic) mania from ‘secondary’ (MS-related) mania is crucial to ensure the correct diagnosis and treatment.
• Key features that distinguish MS-related mania from organic mania include:
  • Late onset, often after age 35–40 years, or onset associated with MS disease progression
  • Weak or absent family history of bipolar disorder
  • Lack of response to standard treatments for bipolar disorder
• Treatment for people with MS who experience bipolar disorder is available and effective. With coordinated care, they can successfully manage their symptoms.

MS affects movement, sensation and other bodily functions, but it also impacts the brain systems involved in thinking, emotions and behaviour. Here, I discuss the relationship between MS and bipolar disorder, a mental health condition that causes episodes of unusually high mood (mania or hypomania) and low mood (depression). Bipolar disorder has received less attention than depression in people with MS, despite its substantial effect on quality of life, treatment adherence and prognosis.

For some people with MS, symptoms of bipolar disorder appear for the first time as their disease develops. In others, existing mood symptoms may be made worse by inflammation, brain lesions or medications used to treat MS. This article explains why bipolar symptoms occur in MS, how they may present, how they can be recognised early and how they can be effectively managed.

How common is bipolar disorder in MS?

Research consistently shows that bipolar disorder is more common in people with MS than in the general population. In the general population, bipolar disorder affects roughly 1–2.4% of people. In MS, studies report current and lifetime prevalence rates of about 3% and 8%, respectively. This means people with MS have approximately double or even treble the usual risk.

Importantly, this increased risk is not simply because people with MS interact with healthcare systems more frequently than the general population, which increases the likelihood of mental health conditions being detected (we call this the ‘admission rate’ bias). Nor is it merely a byproduct of the stress of chronic illness (which might explain depression). Large studies that compare people with MS to similar individuals without MS still show a higher rate of bipolar disorder in the MS group. This suggests the association is real and probably related to changes in the brain caused by MS.

What factors cause MS-related mania?

Researchers believe there are three main mechanisms that drive cognitive and behavioural changes in MS; they can occur alone or together.

• MS lesions that affect mood-regulating circuits
• inflammation and immune changes
• treatment-related factors.

Understanding these mechanisms allows clinicians to distinguish MS-related mania from ‘primary’ (organic) psychiatric illness and to deliver appropriate management.

MS lesions that affect mood-regulating circuits

This mechanism disrupts the ‘hardware’ that controls mood. MS causes inflammation and lesions (scarring) in the brain. Areas that are especially important for controlling emotions and behaviour include:

• the right orbitofrontal cortex (OFC) – involved in regulating social behaviour, judgement and impulse control
• the temporal lobes – important for memory and emotional processing
• the white-matter pathways that connect these regions with deeper emotional and reward centres such as the amygdala and thalamus.

If MS lesions interfere with these circuits, the balance between emotional impulses and rational control can be disrupted. This may lead to behaviours that are characteristic of mania, including disinhibition (reduced ‘internal brakes’), uncontrolled emotions, euphoria (unusually elevated mood) and impulsivity. This pattern is sometimes called secondary mania (mania caused directly by a brain condition such as MS).

There is evidence that right-sided frontal or temporal injury leads to mania-like behaviours in other conditions (e.g. stroke, traumatic brain injury, tumours).

Understanding right- and left-sided brain functions

Consistent with literature on secondary mania from stroke or tumours, MS-associated mania is most often associated with right-sided brain lesions. The right hemisphere is dominant for processing negative emotions and withdrawal behaviours, while the left hemisphere processes positive emotions and approach behaviours. A lesion in the right hemisphere may impair the processing of negative emotions, leading to an unopposed ‘positive’ or euphoric affect (‘highs’) driven by the intact left hemisphere.

Inflammation and immune changes

During MS relapses or periods of immune activation, inflammatory molecules disrupt how brain cells communicate (think of it as a disruption to the brain’s ‘software’). One important system involved is the kynurenine pathway, which controls how the body uses tryptophan (an amino acid essential for the creation of compounds such as serotonin and melatonin).

Inflammation increases the activity of an enzyme called indoleamine 2,3-dioxygenase. This shifts tryptophan away from serotonin production towards production of quinolinic acid, a substance that overly stimulates nerve cells through NMDA receptors (N-methyl-D-aspartate receptors). This ‘excitatory overload’ can lead to symptoms like those seen in primary mania, such as agitation, mood instability, sleep disturbance and racing thoughts.

The kynurenine pathway in inflammation-induced pathology of the central nervous system. Activation of IDO in peripheral immune cells (e.g. macrophages) or in the brain leads to production of kynurenine. This is converted to kynurenic acid in astrocytes and to quinolinic acid in microglia. Kynurenic acid can block the release of glutamate and dopamine, contributing to cognitive dysfunction. Quinolinic acid, by contrast, can increase glutamate release, which contributes to neurodegeneration. Figure modified from Haroon et al.

3-HAO, 3-hydroxy-anthranilic acid oxygenase; IDO, indoleamine-2,3-dioxygenase; KAT II, kynurenine aminotransferase II; KMO, kynurenine-3-monooxygenase; NMDA, N-methyl-D-aspartate.

This pathway is one of the clearest biochemical links between MS inflammation and bipolar-type symptoms.

Treatment-related factors

Some medications used in MS influence mood and may contribute to manic symptoms.

Steroids

High-dose intravenous methylprednisolone, typically 1000 mg/day for 3–5 days, is the most common cause of drug-induced mania in MS. Up to 12% of people treated with corticosteroids experience symptoms of mania, and nearly 65% of those with psychiatric side effects present with a mix of mania and psychosis.

A history of prior steroid-induced mood changes, female sex, older age and higher steroid doses increase risk. Steroid-induced mania typically appears 3 − 4 days after starting treatment (median 11 days in some studies) and may involve:

• severe insomnia
• pressured speech
• irritability or agitation
• grandiosity
• psychosis in severe cases.

Symptoms usually resolve when the dose is tapered (within roughly 3 weeks), but they can persist longer in individuals with underlying bipolar disorder. I therefore try to avoid treating MS relapses with steroids. However, this is not always possible.

Other agents that may cause mania

• Amantadine, used for fatigue, can trigger mania in susceptible individuals.
• Modafinil and methylphenidate, also used for fatigue, have been linked to sudden switching between manic and depressive symptoms.
• Cannabinoids may destabilise mood or cognition.
• Interferons more commonly cause depression than mania, but irritability, aggression and mania have been reported. The risk of new psychiatric symptoms is low, and patients with stable mood disorders can usually tolerate interferons with careful monitoring.
• Fingolimod is linked to mood changes; severe rebound inflammatory activity after discontinuation could theoretically trigger mania.

Diagnosis of MS-related mania

Distinguishing between primary bipolar disorder, secondary MS-related mania and steroid-induced mania can be difficult. Accurate diagnosis is essential for effective management, as treatment for one form may exacerbate another. Below are some of the ‘atypical’ features of MS-related mania that deviate from classic bipolar disorder.

Late onset of symptoms

Primary bipolar disorder usually begins in adolescence or early adulthood. In contrast, secondary mania associated with MS can appear later, often after age 35–40 or during disease progression. A manic or psychotic episode may sometimes be the first manifestation of MS, occurring months or years before a neurological diagnosis.

Mania coinciding with an MS relapse

A sudden change in mood, sleep or behaviour that coincides with new neurological symptoms (e.g. numbness, vision changes, weakness) may indicate that inflammation or new lesions are affecting mood circuits. There may also be evidence of disease progression from MRI scans.

Weak family history

Primary bipolar disorder often runs in families; the absence of a family history suggests a secondary cause (i.e. MS-related pathology).

Disproportionate cognitive decline

Impulse control and executive functions, such as planning, organising and paying attention, are impaired – possibly reflecting frontal lobe involvement.

Mania as an MS relapse

A minority of patients present with isolated psychiatric symptoms (mania, psychosis, delirium) as the only manifestation of a relapse. MRI often reveals new frontal or temporal lesions, even when motor or sensory signs are absent.

Lack of response to standard treatments

Failure to respond to standard mood stabilisers, or paradoxical worsening with antidepressants, warrants a re-evaluation for organic causes.

Genetic considerations

Is the risk solely environmental (inflammation/lesions), or do MS and bipolar disorder share a genetic root? The Major Histocompatibility Complex (MHC) on chromosome 6 is the primary genetic risk factor for MS (specifically the HLA-DRB1*15:01 allele). Interestingly, Genome-Wide Association Studies have suggested that the MHC region is also involved in bipolar disorder and schizophrenia. There is some evidence that, in certain familial clusters, a gene located near the HLA locus (possibly involving the HLA-DR2 antigen) could confer susceptibility to both autoimmune demyelination and bipolar disorder. Other studies have indicated the opposite: that specific MS risk alleles in the HLA region are associated with decreased schizophrenia risk. The results are therefore mixed; some haplotypes may increase the risk of severe mental illness, while others appear protective against it. It is likely that environmental factors (inflammation, lesion burden) play a greater role than genetics in most cases.

Is the risk solely environmental (inflammation/lesions), or do MS and bipolar disorder share a genetic root? The Major Histocompatibility Complex (MHC) on chromosome 6 is the primary genetic risk factor for MS (specifically the HLA-DRB1*15:01 allele). Interestingly, Genome-Wide Association Studies have suggested that the MHC region is also involved in bipolar disorder and schizophrenia.

There is some evidence that, in certain familial clusters, a gene located near the HLA locus (possibly involving the HLA-DR2 antigen) could confer susceptibility to both autoimmune demyelination and bipolar disorder. Other studies have indicated the opposite: that specific MS risk alleles in the HLA region are associated with decreased schizophrenia risk. The results are therefore mixed; some haplotypes may increase the risk of severe mental illness, while others appear protective against it. It is likely that environmental factors (inflammation, lesion burden) play a greater role than genetics in most cases.

Management

Treatment of MS-related mania depends on the cause.

Steroid-induced mania

If steroids triggered the symptoms, the steroids should be tapered or discontinued if safe.
Short-term antipsychotic medications, such as quetiapine, olanzapine or risperidone, can help stabilise mania symptoms. Quetiapine has the added benefit of aiding sleep, which is commonly disrupted in people with MS. Use of low-dose benzodiazepines during the steroid course can help to reduce the insomnia that often precedes or triggers mania.

Mania caused by MS inflammation

If mania is part of an organic, MS relapse, treating the inflammation is important. High-dose steroids may then be necessary, even though they can in other circumstances cause mania.
This crucial distinction underscores the need for close coordination between neurology and psychiatry.

Mood swings

Lithium is still the gold standard mood stabiliser and is generally safe for psychiatric management in MS. The anticonvulsants valproate, lamotrigine and carbamazepine are useful alternatives in people with MS; they treat both the mania and other MS-related comorbidities, such as neuropathic pain and trigeminal neuralgia.

Managing future steroid treatment

People with a known history of bipolar disorder or steroid-induced instability may benefit from:

• starting a low-dose mood stabiliser (e.g. lithium) before the steroid course
• adding an antipsychotic temporarily (e.g. olanzapine)
• using sleep support (e.g. low-dose benzodiazepines) to prevent insomnia (a common trigger for mania).

Long-term management

Any MS patient presenting with new-onset mania requires a comprehensive workup, including MRI (to check for new frontal/temporal lesions) and a review of recent medication changes, rather than a direct referral to psychiatry. Ongoing coordination between neurologists and psychiatrists is, however, essential. A neurologist might misinterpret mania as ‘euphoria’ related to frontal lobe damage (pseudobulbar affect), while a psychiatrist might miss the neurological signs of an MS relapse that is driving the mood change. Screening tools (e.g. Mood Disorder Questionnaire) may help identify individuals at higher risk but should not replace clinical judgement.

Recognising the distinguishing features of MS-related mania allows clinicians to intervene promptly, reduce misdiagnosis and optimise care. With integrated neurological and psychiatric management, most people with MS experiencing bipolar symptoms can achieve stable, effective control of their mood and maintain a high quality of life.

Reference

Haroon, E et al. Psychoneuroimmunology meets neuropsychopharmacology: translational implications of the impact of inflammation on behavior. Neuropsychopharmacology Rev; 2011:1–26.