Weakness Flashcards
When a patient presents with apparent generalized motor deficits, you should always check. . .
. . . the bulbar muscles: those innervated by cranial nerves and the corticobulbar tract.
This can differentiate between generalized NMJ disease and lesions of the corticospinal tract
ALS
- Amyotrophic lateral sclerosis
- Most common motor neuron disease
- Affects the motor system centrally and peripherally, and involves the bulbar muscles and respiratory muscles
- Has multiple variants
- Generally age > 50, prognosis generally 2-3 years after diagnosis
- Most sporadic, some familial
- Weakness starts in one limb and progresses to be more generalized
- Pseudobulbar affect observed in later stages
- Eye movements and continence last muscle functions to be affected
ALS on exam
- Combination of upper and lower motor neuron signs
- Tongue fasciculations are classical, but not always present
- May co-occur with frontotemporal dementia
- Pseudobulbar affect may be present
Pseudobulbar affect
Laughing and/or crying out of proportion to the emotion felt
Primary lateral sclerosis
Pure central nervous system/upper motor neuron variant of ALS
Progressive muscular atrophy
Pure peripheral nervous system/lower motor neuron variant of ALS
Progressive bulbar atrophy
Pure brainstem variant of ALS
Etiologies of muscle disease
- Inflammatory:
- polymyositis, dermatomyositis, inclusion body myositis, immune-mediated necrotizing myopathy
- Medications:
- most commonly statins and corticosteroids
- Systemic diseases:
- HIV, endocrine disease, rheumatologic disease, critical illness
- Genetic disorders
Diseases of muscle are distinguished from central nervous system or peripheral nervous system causes of weakness by . . .
Diseases of muscle are distinguished from central nervous system or peripheral nervous system causes of weakness by lack of upper or lower motor neuron signs, lack of sensory changes, and by the pattern and distribution of weakness.
Symmetric proximal weakness
- Most common weakness pattern in diseases of muscles
Myopathy with only distal limb involvement on exam
Suggests one of the distal myopthies
Mostly genetic disorders
Asymmetric myopathy with both proximal and distal limb involvement on exam
Suggests inclusion body myositis
Insidiously progressing autoimmune weakness vs rapidly progressing autoimmune weakness
Insidious: Polymyositis, dermatomyositis
Rapid: immune-mediated necrotizing myopathy
When weakness is exercise–induced, diseases of ___ must also be considered
When weakness is exercise–induced, diseases of the neuromuscular junction must also be considered
Fundamentally, reflexes are proportional to ___.
Fundamentally, reflexes are proportional to muscle tone.
Lesions that cause hypoactive vs hyperactive reflexes
Hypoactive: lower motor neuron lesions, affrent sensory neuron lesions
Hyperactive: upper motor neuron lesions,
How to diagnose weakness
- Make sure it is true weakness
- Identify which muscles are weak, and how weak the muscles are relative to each other
- Identify associated signs and symptoms
- Evaluate for LMN signs, UMN signs, and reflexes on exam
- Diagnostic test based on hypothesis
Clinical guide for localizing weakness
Metabolic etiologies of peripheral neuropathy
- Diabetes mellitus (sorbitol accumulation or vascular)
- B12 (cobalamine) deficiency
- B6 (pyridoxine) excess
- B6 deficiency
- B1 (thiamine) deficeincy
Charcot Marie Tooth syndrome
- Common form of hereditary polyneuropathy
- Autosomal dominant
- Usually starts < age 10
- Sensory and motor deficits
- Characteristic exam findings:
- High arched foot
Guillain Barre Syndrome
- Acute onset, rapidly progressive muscle weakness
- Autoimmune etiology
*
Allodynia
Even light touch is painful
Small fiber neuropathy
- Largely affects C-fibers, which carry pain information
- Stabbing, shooting, burning pain, often with allodynia
- May occur with DM, chronic alcohol use, HIV, or amyloidosis
Large fiber neuropathy
- Affects larger sensory fibers carrying vibration and proprioception
- Parasthesias, decreased vibratory sense, decreased proprioception
- Etiologies include B12 deficiency, Sjorgren’s
Carpal tunnel syndrome
- Mononeuropathy of the median nerve
- Tingling/numbness in the median nerve distribution
- Worse at night
Ulnar neuropathy
- Distal injury characterized by an “ulnar claw”, while proximal injury is characterized by inability to flex the fingers of the ulnar claw
- Sensation in this area also affected in both cases
Erb Duchene syndrome aka Erb’s palsy
- Plexopathy of the brachial plexus
- “Waiter’s tip” posture of arm on affected side
- Horner’s syndrome on affected side
- May be due to birth injuries, and be seen in infants
“Saturday night palsy”
- Called such because people who sleep heavily on saturday night may sleep on their arm in such a way to cause this
- Radial nerve mononeuropathy caused by clenching of nerve at spiral groove
- Wrist extensors are paralyzed, resulting in tonic wrist drop
Klumpe’s palsy
- Plexopathy caused by birth injury
- Fingers tonically flexed, often elbow tonically flexed as well and arm held to chest
“Hand signs” for medial and ulnar injuries
