Multiple Sclerosis
Multiple sclerosis (MS) is the classic diagnosis involving upper motor sensory pathways, characterized by demyelinating lesions affecting the central nervous system's white matter tracts including the posterior columns and other ascending sensory pathways. 1
Pathophysiology and Clinical Features
MS affects central sensory pathways through demyelination of white matter tracts in the brain and spinal cord, leading to characteristic sensory disturbances 1:
- Posterior column involvement causes loss of discriminative touch, proprioception, and vibration sense, resulting in ataxia and impaired fine motor control 2
- Patients experience disturbances in knowledge of movement and position, with clumsiness particularly affecting hand function 2
- Spinothalamic pathway lesions can occur, affecting pain and temperature sensation, though isolated posterior column lesions are more characteristic 2
Diagnostic Approach
The diagnosis requires demonstration of dissemination in space (DIS) and dissemination in time (DIT) using MRI criteria 1:
- At least one clinical event consistent with acute demyelination is mandatory - MRI findings alone cannot establish MS diagnosis 1
- DIS requires lesions in at least 2 of 4 CNS regions: periventricular, cortical/juxtacortical, infratentorial, and spinal cord 1
- DIT can be demonstrated by simultaneous gadolinium-enhancing and non-enhancing lesions, or new T2/gadolinium-enhancing lesions on follow-up MRI 1
Critical Diagnostic Pitfalls
Radiologically isolated syndrome (RIS) presents a diagnostic challenge 1:
- Incidental brain lesions meeting Barkhof criteria for DIS do not constitute MS without clinical symptoms 1
- Approximately one-third of RIS patients develop neurological symptoms within 5 years, particularly those with gadolinium-enhancing or spinal cord lesions 1
- Risk factors for progression include oligoclonal bands, younger age, male sex, abnormal visual evoked potentials, and asymptomatic spinal cord lesions 1
Differential diagnosis exclusion is imperative before confirming MS 1:
- Neuromyelitis optica spectrum disorders must be excluded, particularly in Asian populations 1
- Imaging "red flags" should prompt reconsideration of alternative diagnoses 1
- The 2010 McDonald criteria apply equally well across different ethnic populations including Asian and Latin American patients 1
Sensory Pathway Specifics
When posterior columns are lesioned in isolation 2:
- Primary light touch and pressure sensation remain intact via spinothalamic pathways 2
- All forms of discrimination are disturbed, including two-point discrimination and texture recognition 2
- Patients may experience lability of threshold, persistence of sensation, and tactile/postural hallucinations 2
- Combined lesions of both posterior columns and spinothalamic tracts cause total loss of tactile and pressure sensibility 2