What is multiple sclerosis?
Multiple sclerosis (MS) is a chronic, inflammatory, immune-mediated disease of the central nervous system (CNS) —brain, spinal cord and optic nerve— in which demyelination, axonal damage and neurodegeneration occur.
This means that not only is the myelin affected, but also the axons, which contributes to physical and cognitive disability over time.
Causes of multiple sclerosis
The exact causes are not fully known, but MS is considered a multifactorial disease, resulting from the interaction between genetics and environmental factors.
The main factors include:
- Epstein-Barr virus (EBV) (key trigger)
- Smoking
- Vitamin D deficiency
- Low sun exposure
- Obesity in adolescence
At the genetic level, the HLA-DRB1*15:01 allele is one of the most relevant risk factors.
MS is currently understood to be the consequence of an abnormal immune response against the CNS in predisposed individuals.
Epidemiology
Multiple sclerosis affects 2.9 million people worldwide.
- Mean age at diagnosis: 30–33 years
- Higher prevalence in women: approximate ratio of 2:1
In Spain, more than 61,700 cases were estimated in 2021, with a prevalence of 132 per 100,000 inhabitants and a higher frequency in the north of the country.
Cognitive involvement in MS
In addition to neurological symptoms, MS can cause cognitive impairment, even in early stages.
The main domains affected are:
- Attention
- Processing speed
- Memory
- Executive functions
- Verbal fluency
It is estimated to affect approximately 1 in every 3 users with relapsing-remitting forms.
Symptoms of multiple sclerosis
Motor symptoms
- Weakness in the limbs
- Spasticity and spasms
- Tremor and loss of balance
- Difficulty walking
Sensory symptoms
- Tingling and numbness
- Electric shock sensation
- Neuropathic pain
Visual symptoms
- Blurred or double vision
- Loss of vision
- Optic neuritis
Bladder and bowel symptoms
- Urinary urgency and incontinence
- Constipation
Sexual symptoms
- Decreased libido
- Difficulties with arousal
Speech and swallowing
- Dysarthria
- Dysphagia
Other frequent symptoms include fatigue, depression, anxiety and cognitive changes. Fatigue is one of the most disabling symptoms.
Relapse vs pseudo-relapse
Relapse: appearance of new symptoms or worsening lasting ≥24 hours without fever or infection.
Pseudo-relapse: transient worsening triggered by factors such as heat, infections or tiredness, without inflammatory activity.
Diagnosis
Diagnosis is based on the McDonald criteria, which require demonstrating:
- Dissemination in space
- Dissemination in time
The following are used:
- Clinical assessment
- Magnetic resonance imaging
- Cerebrospinal fluid
Recent advances include:
- Oligoclonal bands
- Kappa free light chains
- Central vein sign
- Paramagnetic rim lesions
This allows for earlier diagnosis, although there is a risk of overdiagnosis.
How the disease progresses
MS can follow different courses:
- Relapsing-remitting (most frequent)
- Secondary progressive
- Primary progressive
Progression without relapses may also occur, known as PIRA.
Treatment
There is no definitive cure, but there are multiple options:
- Corticosteroids for relapses
- Plasmapheresis in severe cases
- Disease-modifying therapies
The approach also includes:
- Physical rehabilitation
- Symptomatic treatment
- Psychological support
- Cognitive assessment and rehabilitation
Cognitive impairment does not always improve with pharmacological treatment alone, which is why neuropsychological intervention is key.
