Comorbid obsessive–compulsive disorder and obsessive–compulsive behaviour are more common than one might realise in people with MS. This section describes in detail how these conditions develop and manifest in MS, with links at the end to download rating scales for self-assessment.
Key points
- People with MS are 3.25 times more likely than healthy controls to develop obsessive–compulsive disorder (OCD) or obsessive–compulsive behaviour (OCB).
- Neurodegeneration that causes the physical disability of MS also disrupts brain circuits responsible for inhibition and emotional regulation. Obsessive–compulsive symptoms therefore become more likely as physical disability in MS increases.
- Specific cognitive deficits associated with OCD further compound the cognitive impairment caused by MS.
- OCD also impacts adherence to MS treatment, leading to missed doses, chaotic dosing or double-dosing.
- Selective serotonin reuptake inhibitors are the mainstay of OCD drug treatment; tricyclic antidepressants areoften used as a second-line treatment.
- Standard psychological therapies for OCD must be adapted to allow for reduced levels of physical stamina and cognitive reserve in many people with MS.
Introduction
People with MS commonly develop psychiatric symptoms over and above the reactive psychological responses to having MS; such comorbidities are often manifestations of the underlying nervous system damage.
Obsessive–compulsive disorder (OCD) and obsessive–compulsive behaviour (OCB) tend to be underdiagnosed in people with MS, and they complicate its management. ‘Organic’ or ‘secondary’ OCD in MS is driven by distinct pathophysiological mechanisms (i.e. factors relating to the underlying MS disease processes and the damage they cause). These mechanisms involve the disruption of cortico-striato–thalamo-cortical circuits (see brain chemistry section below), atrophy of grey matter in specific, key areas of the central nervous system (CNS), and a proinflammatory environment. The clinical implications of OCD may be significant and are associated with greater physical disability, a higher disease burden and, often, poor adherence to medication.
Clinical symptoms of OCD in people with MS
OCD in people with MS is characterised by obsessions and compulsions – similar to its presentation in the wider population. In MS, however, OCD often carries distinct nuances related to an individual’s experience of the disease. For example, unpredictable, fluctuating sensory symptoms (paraesthesias, numbness, pain) may develop into obsessive ‘body checking’. A benign itch or twitch may be catastrophised as a new relapse, leading to compulsive reassurance-seeking from medical providers, repeated self-examinations or excessive researching of symptoms. This overlaps with, but is distinct from, illness anxiety disorder due to the presence of ritualised behaviours.
Given that many people with MS are taking an immunosuppressive disease-modifying therapy (DMT), fears of infection are rational. However, in OCD, these fears become excessive and incompatible with an individual’s true self. A person with MS may engage in ritualised hand-washing or sterilisation of their environment that goes far beyond medical necessity, causing skin damage or social isolation. The distinction between prudent caution and compulsion is often defined by the level of distress and the rigidity of the behaviour.
Cognitive deficits in people with MS, particularly in working memory, can exacerbate checking rituals. Someone with MS may repeatedly check whether the stove is off, not purely out of anxiety, but because they genuinely cannot retain the act of turning it off in their working memory. This double deficit of anxiety plus amnesia makes checking rituals particularly resistant to standard cognitive interventions. OCD is associated with specific cognitive deficits, particularly in executive function. In MS, these deficits overlap with the disease’s own cognitive burden, creating a compound impairment.
A case scenario
| I am 44 years of age, and I have had MS for 16 years. I was on fingolimod before switching to ocrelizumab. I have weakness in both legs and can manage about 200 yards with a stick. I also have bladder and bowel problems. Over the last few years, I have developed obsessive–compulsive symptoms. I have a germ phobia and can’t touch anything; I keep washing my hands, so they are raw from using soap and alcohol spray. As a solution, I have started using latex gloves when I go out. I also started worrying about my ocrelizumab infusion being contaminated, and this caused me to have a panic attack. My family doctor has started me on fluoxetine and has referred me to see a psychiatrist. |
The need for symmetry or exactness is another feature of MS-related OCB. This may be related to subtle sensorimotor deficits or to the disruption of error-processing networks in the cerebellum and basal ganglia.
Both OCD and MS are associated with impairments in response inhibition and in set-shifting (cognitive flexibility, or task switching). A person with MS and comorbid OCD may show profound difficulties in shifting gears mentally. Once an obsessive thought enters the stream of consciousness, the brakes (inhibition) fail and the steering (set-shifting) locks, leading to cognitive rigidity and perseverance. Research suggests that memory impairments in OCD are often secondary to executive dysfunction (problems with organising information during encoding) rather than to primary retrieval deficits. In MS, both primary retrieval deficits (from hippocampal/temporal lobe damage) and secondary executive deficits (due to frontal lobe damage) can occur.
OCD prevalence and risk factors
The odds of developing OCD are estimated to be 3.25 times higher in people with MS than in healthy controls. While the lifetime prevalence of OCD in the general global population is around 1.3–3%, studies in MS cohorts consistently report higher rates. A meta-analysis of 10 studies established a pooled prevalence of OCD among people with MS of almost 11%.1 OCB is not a rare but a frequent psychiatric complication of MS, and it is comparable in impact, if not incidence, to both depression and anxiety.
Causes, risk factors and prevalence of primary OCD and secondary MS-related OCD compared.
OCD in the general population often starts either in childhood or in early adulthood and exhibits gender variances depending on the age of onset. However, in the context of MS, there is no correlation between gender and the presence of OCD. There is also no correlation between OCD frequency and age of onset, educational level or marital status within MS cohorts.
In idiopathic OCD (that arises without a known underlying medical cause), family history is an important risk factor, with high heritability rates. Data in MS populations is mixed. Some studies report no significant correlation between comorbid OCD–MS and a positive family history of OCD; this supports the hypothesis that the psychiatric symptoms are secondary to the neurological damage from MS rather than a primary genetic disorder. Conversely, some studies hint at shared genetic vulnerabilities, suggesting that MS may unmask a latent genetic predisposition.
Development of OCD in people with MS
The development of OCD in the MS population is significantly correlated with a rise in EDSS (Expanded Disability Status Scale) scores, indicating that as physical disability accumulates, so does the prevalence of obsessive–compulsive symptoms. This correlation challenges the notion of OCD as merely a psychological reaction to illness; rather, it implies that the neurodegeneration due to MS, driving motor and sensory disability, is simultaneously affecting the neuronal circuits responsible for cognitive inhibition and emotional regulation.
OCD development is also positively correlated with the duration of MS disease; people with a long history of MS have a higher lesion burden and greater brain atrophy than those recently diagnosed, which increases the probability of damage to OCD-relevant networks. Specific neurological deficits are strongly associated with OCD, including cerebellar, sensory, motor and cranial nerve involvement. The cerebellar association is intriguing, given the cerebellum‘s emerging role in the cerebellar cognitive affective syndrome, where damage leads to deficits in executive function and emotional control similar to those seen in OCD.
Effects of MS on brain chemistry
The cortico-striato-thalamo-cortical network is a region of the brain that normally helps us regulate repetitive actions, recognise mistakes and dismiss unwanted thoughts or behaviours. This network links the areas involved in decision-making (orbitofrontal cortex), emotional control (anterior cingulate cortex), and regulation of voluntary movements (basal ganglia). Hyperactivity and dysfunction within these circuits contribute to the development of ‘idiopathic’ or primary OCD. The causes of OCD in people with MS, however, differ from those seen in primary OCD. In MS, OCD is thought to result mainly from the effects of inflammation and damage within the brain and nervous system.
Damage to the brain caused by MS lesions, nerve fibre loss, and shrinkage of brain tissue can interrupt these cortico-striato-thalamo-cortical circuits at several points. Research has shown that people with both MS and OCD tend to have loss of brain volume in areas involved in self-control, flexible thinking and emotional processing. One important region affected is the inferior frontal gyrus, which helps the brain stop inappropriate thoughts or actions. Damage here may make it harder to suppress intrusive thoughts (obsessions) or stop repetitive behaviours (compulsions). Other affected regions are connected to the brain’s emotional centres (the temporal lobes and limbic system). Damage in these areas may contribute to the intense anxiety, uncertainty and persistent doubt that are common in OCD.
OCD symptoms in primary, idiopathic MS are thought to arise from suppression of the normal inhibitory signals from the basal ganglia (resulting in ‘disinhibition’). In MS, inflammatory lesions and iron deposition occurring within the basal ganglia cause tissue damage that may interfere with the brain’s ability to block (or inhibit) repetitive or unwanted thoughts and actions – creating problems like those seen in primary OCD.
MS may also damage the white matter pathways (the cingulum bundle and the uncinate fasciculus) that connect different brain regions, including the pathway linking the emotional centres with brain areas responsible for judgement and decision-making. Damage in this area may alter emotional processing, leading to abnormal interpretation of intrusive thoughts.
Immune activity in the CNS associated with MS may also contribute to psychiatric symptoms through the release of inflammatory chemicals called cytokines. These chemicals can interfere with neurotransmitters, particularly serotonin, which plays a key role in OCD.
Normally, the body uses a substance called tryptophan to produce serotonin. However, inflammation in MS increases the activity of the enzyme indoleamine 2,3-dioxygenase (IDO), which shifts tryptophan away from serotonin production towards a chemical pathway that produces quinolinic acid. The resulting overstimulation of nerve cells may reduce serotonin levels in the brain and produce potentially harmful, neurotoxic substances.
Studies of patients with MS-related OCD have demonstrated reduced serotonin levels in the cerebrospinal fluid, supporting the idea that inflammation and serotonin disruption are both involved in OCD.
There may also be some shared genetic vulnerability between MS and OCD. Researchers are continuing to investigate several genes that may increase susceptibility to both conditions, notably STAT3 (Signal Transducer and Activator of Transcription 3) and NTRK2 (Neurotrophic Receptor Tyrosine Kinase 2).
Impact of OCD on the management of MS
Impact on treatment adherence
One of the most clinically significant aspects of comorbid OCD in MS is its impact on adherence to disease-modifying treatment. For people with MS on injectable DMTs (e.g. interferon beta-1a, glatiramer acetate, ofatumumab), obsessive fears regarding needles can lead to severe or ritualised avoidance behaviours. While ‘injection anxiety’ is common, in OCD it manifests as catastrophic thinking about the injection process (e.g. ‘If I hit a vein, I will die’). The anticipatory anxiety can trigger panic attacks, leading to missed doses.
People with MS with contamination obsessions may view their medication as ‘toxic’ or ‘impure’. This is particularly relevant for infusion therapies such as ocrelizumab, ublituximab and natalizumab, where the recipient has no control over the environment’s sterility. They may also fear that the medication is permanently altering their body in a ‘contaminated’ way, leading to non-adherence driven by a desire for body purity.
Effects of irregular dosing on DMT efficacy
The ‘doubt’ inherent in OCD can lead to chaotic dosing. People with MS may obsess over whether they took their pill, leading to either missed doses (from fear of accidental overdose) or double-dosing (from fear of missing a dose). For oral DMTs with short half-lives, this inconsistency can compromise efficacy. Patients may misinterpret benign physiological sensations (e.g. a headache or flush) as severe adverse events or allergic reactions, leading to premature discontinuation of therapy.
Conversely, dimensions of OCD that overlap with perfectionism or symmetry can lead to hyper-adherence. People with MS who rely on strict daily rituals may incorporate medication-taking into an immutable schedule. Never missing a dose, they appear to be ‘model patients’; an inflated sense of responsibility (a core cognitive distortion in OCD) may lead them to feel that missing a dose is a moral failure or will cause immediate, catastrophic disability. However, this ‘good’ adherence is pathological if it comes at the cost of extreme distress. An MS patient who has a panic attack because they took their medication 10 minutes late is adherent, but they are not well. Healthcare professionals (HCPs) must look beyond the adherence rate to the quality of the patient’s engagement with their treatment.
Differential diagnosis
Distinguishing organic OCD, secondary to MS, from a primary psychiatric disorder is important for management. MS-related OCD often starts late in life or coincides with an MS relapse or the appearance of new lesions on magnetic resonance imaging (MRI). Patients with organic OCD may have less ‘insight’ into the senselessness of the behaviour or be resistant to standard monotherapy with a selective serotonin reuptake inhibitor (SSRI). The standard classification systems of mental disorders, DSM-5 and ICD-11, increasingly recognise OCD due to other medical conditions. Key flags for organic OCD include:
- its temporal relationship to the neurological condition
- the presence of atypical neurological signs, e.g. subtle movement disorders or frontal release signs (these involuntary reflexes are suppressed as an infant’s brain matures but may return if the frontal lobes are damaged and inhibitions are ‘released’)
- other focal neurological signs or symptoms of localised damage.
Clinical characteristics and MRI findings of primary OCD and secondary MS-related OCD compared.
EDSS, Expanded Disability Status Scale; MRI, magnetic resonance imaging.
Drug treatment
The pharmacological management of OCD in MS requires navigating the complex interactions between DMTs and psychotropic medications, primarily SSRIs and TCAs (tricyclic antidepressants).
Psychotropic medications: important interactions
SSRIs are the mainstay of OCD treatment; agents such as sertraline, fluoxetine, paroxetine and fluvoxamine are commonly used. However, their side effect profiles can mimic or exacerbate MS symptoms. A common side effect is that they can worsen the fatigue already present in MS. SSRIs can also worsen MS-related sexual dysfunction (erectile dysfunction, loss of sensation). Some SSRIs and TCAs have anticholinergic properties that can worsen urinary symptoms and trigger urinary retention.
Clomipramine, a TCA with potent serotonergic effects, is often used as a second-line treatment for OCD. However, its anticholinergic burden is high. It should be used with caution in patients with significant dysfunction of the autonomic nervous system.
MS DMTs: important interactions
Siponimod, a sphingosine-1-phosphate (S1P) receptor modulator used in secondary progressive MS (SPMS), is extensively metabolised by hepatic enzymes (CYP2C9 and CYP3A4). Fluvoxamine, an SSRI used to treat OCD, is a potent inhibitor of CYP1A2 and a moderate-to-strong inhibitor of both CYP2C9 and CYP3A4. Co-administration blocks siponimod’s metabolic clearance; the resulting elevated siponimod levels could increase the risk of bradyarrhythmia and lymphopaenia. Therefore, fluvoxamine should not be used in people with MS on siponimod. Alternative SSRIs with low CYP inhibition potential (e.g. citalopram, escitalopram) are preferred.
Initiation of fingolimod (another S1P modulator) is associated with transient bradycardia and AV conduction delays. It can also prolong the QT interval. Many SSRIs, particularly citalopram (and to a lesser extent escitalopram and fluoxetine), cause dose-dependent QT interval prolongation, which increases the risk of Torsades de Pointes and sudden cardiac death. Therefore, a pre-treatment electrocardiogram is mandatory. If citalopram is needed in someone on fingolimod, the dose should be limited to a maximum of 20 mg/day in adults and 10 mg/day in the elderly. Sertraline or paroxetine are safer cardiac alternatives to co-administer with fingolimod.
Ozanimod, an S1P modulator, has active metabolites (CC112273 and CC1084037) that inhibit monoamine oxidase B (MAO-B) in vitro (e.g. in the laboratory setting). Therefore, combining an inhibitor of MAO (which prevents the breakdown of serotonin) with serotonergic drugs (SSRIs, TCAs and SNRIs [serotonin and norepinephrine reuptake inhibitors]) theoretically risks the serotonin syndrome (hypertensive crisis, hyperthermia, myoclonus). While ozanimod’s label carries a warning against coadministration with MAO‑B inhibitors, the potential for interaction has not been studied and clinical data suggest that MAO-B inhibition is weak.
Psychological therapy
Cognitive behavioural therapy (CBT) with exposure and response prevention (ERP) is a standard psychotherapy for OCD. However, standard protocols assume a level of physical stamina and cognitive reserve that many people with MS lack. Successful treatment requires significant adaptation.
Fatigue is the most common and debilitating symptom of MS. ERP is cognitively and emotionally exhausting; a standard 50-minute session involving high-intensity exposure can trigger ‘post-exertional malaise’ or a ‘cognitive crash’ in people with MS. Therefore, exposures must be graded not just by anxiety level but by energy expenditure. Micro-exposures (shorter duration) may be necessary. Sessions and homework should be scheduled during the patient’s peak energy window (often mid-morning). Therapists should integrate spoon theory or energy conservation techniques into the ERP plan (e.g. sitting during exposures if standing causes fatigue).
Executive dysfunction can hinder the cognitive component of CBT (e.g. the need to challenge irrational thoughts) and a person’s ability to remember their behavioural homework. Therapy should rely less on abstract cognitive restructuring and more on concrete behavioural change. Use of written summaries, smartphone reminders and visual cues can be helpful.
Involving a caregiver to act as a ‘co-therapist’ can help reinforce homework and prevent avoidance, particularly if the patient has memory deficits. Reducing the complexity of cognitive interventions and focusing on pure ‘behavioural extinction’ (i.e. gradually weakening and eventually eliminating an unhelpful learned behaviour, using ERP) is often more effective than CBT alone in patients with cognitive impairment.
In patients with significant disability, some exposures (e.g. touching a public bathroom door) may be physically impossible. Utilising detailed scripts to vividly imagine the feared scenario and resist the compulsive mental ritual are primary tools. Emerging virtual reality therapies simulate environments (e.g. a dirty kitchen) for homebound or wheelchair-dependent patients, allowing controlled exposure without physical risk.
Group CBT can be highly effective for people with MS and OCD. The group format provides validation by reducing the isolation that comes with having two diseases; seeing others with disabilities successfully engage in ERP can also help.
Recommendations
Routine screening of people with MS, particularly those with EDSS scores > 3.0 or long disease duration, may help identify those with OCD and OCB. Standard screening tools include the Yale-Brown Obsessive Compulsive Scale (Y-BOCS) or the Obsessive Compulsive Inventory Revised (OCI-R).
You can download the Y-BOCS and OCI-R and rate yourself.
The Y-BOCS score breakdown is as follows:
- 0–7: Subclinical (no significant symptoms)
- 8–15: Mild OCD
- 16–23: Moderate OCD
- 24–31: Severe OCD
- 32–40: Extreme OCD
For the OCI-R, a cutoff score of 12 is used to estimate the likelihood of an OCD diagnosis (sensitivity 82%, specificity 83%).
People with MS and HCPs must remain vigilant about MS-related OCD in patients with adult-onset symptoms, atypical presentations or new temporal/frontal lesions on MRI. If you have MS and need treatment for OCD, please ask your therapists to modify CBT and ERP to include pacing for fatigue and possible simplification in case of executive dysfunction. HCPs should specifically ask patients if they experience needle phobia, contamination fears or obsessive doubting as barriers to DMT adherence.
Reference
- Mirmosayyeb O, et al. Obsessive-compulsive disorder in people with multiple sclerosis: a systematic review and meta-analysis. Acta Neurol Belg 2026. doi: 10.1007/s13760-026-02990-5.

