Neurology - Weakness Flashcards
Important clinical features in assessing weakness
- Truly weak? (psychological)
- Pattern of limb involvement (1, 2 or 4)
- Side (level) of the lesion (e.g. higher CNS dysfunction? CN palsies? UMN or LMN signs?)
- Speed of onset (most important!)
Sudden onset weakness is likely to be vascular
Slower onset could be many other pathologies
What is true weakness?
Weakness is a term that is often used by patients to mean fatigue or tiredness.
True weakness leads to loss of function (but this can also occur in sensory loss and cerebellar disease).
Ask the patient to list the specific activities that cannot be performed (e.g. walking, climbing, combing their hair etc)
Features of upper motor neurone lesions?
These usually occur in the pyramidal tract
Pattern of weakness is contralateral to the side of the lesion:
- Incomplete weakness affecting large movements
- Extensors of upper limb and flexors of lower limb (causing hemiplegic gait)
Tone is spastic = velocity dependant resistance to movement
- Clasp knife
- Clonus
Brisk reflexes
Atrophy but no wasting or fasciculation
What are the characteristics of extrapyramidal or basal ganglia disorders?
There is no true loss of muscle power but a failure of integration of agonist and antagonist muscles. Patients will have involuntary movements (“dyskinesias”).
Basal ganglia lesions manifest at rest (cf. cerebellar lesions which appear on intention)
Rigidity = velocity independent increase in resistance to movement - e.g. lead pipe or cog wheeling (rigidity + tremor)
Normal reflexes
Normal muscle appearance
Features of a lower motor neuron lesion
Pattern of weakness:
- Usually marked, affecting specific muscle groups
- Maximal distally in polyneuropathies
Tone:
- Hypotonia (flaccid paralysis)
Reflexes:
- Reduced or absent (due to interruption of the reflex arc)
Wasting and fasciculation (if lesion at the level of the anterior horn cell)
What are the features of weakness caused by muscle disease?
Pattern of weakness is usually generalised (unless one muscle is injured)
- Maximal proximally and usually symmetrical: neck and swallowing and eye muscles may be involved
Tone may be normal or decreased
Normal reflexes
Normal or atrophic appearance
Features of neuromuscular junction disease
Weakness is variable but fatigable (key feature), ptosis and extraocular muscle weakness is common
Tone - normal
Reflexes - normal or depressed (Lambert-Eaton)
Appearance of muscle is usually normal
What is weakness in all 4 limbs called and what could cause it?
Quadraparesis = weakness in all 4 limbs
Causes:
- CNS lesions - very unlikely if conscious level is normal
- Nerve roots - e.g. malignant meningitis
- Spinal cord lesion
- Peripheral nerve disease - e.g. GBS or other polyneuropathy
- Muscle disease - e.g. inflammatory, metabolic or inherited
What brainstem lesions can cause weakness in all 4 limbs?
Pontine haemorrhage or other lesion can lead to complete quadriplegia, including the face (locked in syndrome) - consciousness is usually very depressed in the early stages
What spinal cord level needs to be affected for all 4 limbs to become weak?
Complete weakness affecting all 4 limbs only occurs if the spinal lesion is above C5
Pathology can be divided based on speed of onset:
- Acute: cord compression, anterior spinal artery thrombosis and acute transverse myelitis
- Subacute: intrinsic spinal cord tumours, vascular malformations of the dura, vitamin B12 deficiency, malignant meningeal infiltration
- Chronic: bening tumours, syringomyelia, inheriated conditions - e.g. hereditary spastic paraparesis (although this usually affects only 1 leg), spinocerebelar ataxia (e.g. Freidrich’s ataxia) and tropical spastic paraparesis caused by HTLV 1 infection
Nerve root pathology causing quadraparesis
Inflammation caused by a viral infection (e.g. CMV, VZV) of nerve roots can cause weakness in all 4 limbs as can malignant infiltration spread through the cerebrospinal fluid (malignant meningitis)
What peripheral polyneuropathies can cause weakness in all 4 limbs?
Diffuse nerve damage:
- GBS
- CIDP
- Inherited neuropathies such as CMT
Others include diphtheria, sarcoidosis, Lyme disease, borreliosis and amyloid
In general there is distal predominant pattern of weakness
What can cause weakness of one limb?
This is a difficult clinical problem and lesions can arise from almost anywhere:
- Cortical lesions affecting motor pathways to the limbs can start as a problem isolated to one limb. Lacunar strokes affecting the basis pontis can cause clumsy hands
- MND - frequently starts in one limb with foot drop or wasting of the intrinsic hand muscles
- Spinal cord lesions (e.g. Brown Sequard, nerve root)
- Plexopathy - e.g. brachial neuritis or diabetic amyotrophy
- Involvement of multiple large motor nerves (mononeuritis multiplex, usually systemic)
- Isolated mononeuropathy
Cause of weakness on one side of the body
This is called a hemiparesis
Cerebral cortex - hemisphere lesion produces contralateral limb weakness + language (if dominant) or neglect (if non dominant)
Internal capsule lesion
Brainstem lesion - vascular occlusion here can cause a number of eponymous syndromes:
- Midbrain - hemiplegia with a contralateral IIIrd nerve palsy (Weber’s syndrome)
- Pons - hemiplegia + conjugate gaze deviation towards the weak limbs and ipsilateral LMN facial weakness
NB - brainstem lesions tend to produce a combination of contralateral weakness and ipsilateral CN palsies
Causes of spastic paraparesis
= UMN signs in both lower limbs
- Spinal cord lesion
- Peripheral neuropathy
- Bilateral involvement of lumbosacral plexus
- MND
- Parasagittal meningioma (very rare)
