8. Peripheral Nervous System Flashcards
A patient presents with a 6-week history of generalized weakness. She says that she wakes up feeling well, but by the end of the day can barely make it up a flight of stairs and has double vision. Sometimes, she has trouble chewing and swallowing her food. On exam she is indeed weak, with bilateral ptosis.
- The most likely diagnosis is…
- What is the pathogenesis?
- You give the patient an appointment in neurology clinic. Which of the following tests will confirm the diagnosis
- But…the patient refuses to leave the ER and demands a diagnosis. The next step in the ER is to…
- The patient becomes severely fatigued. On exam, she is tachypneic and has trouble counting to 10 in one breath. What is the patient experiencing?
- What is the next step in treating this patient?
- Myasthenia gravis (MG)
- Autoantibodies against postsynaptic Acetylcholine receptors
- EMG under repetitive stimulation
- Give a trial of edrophonium = Tensilon test
- Myasthenic crisis
- Intubate the patient
Myasthenia gravis (MG)
- An autoimmune neuromuscular junction disorder where antibodies attack postsynaptic acetylcholine receptor
- Epidemiology
- 2 peaks: age 20-30 and age 60-80
- Women > men
- Signs and symptoms
- Fluctuating symptoms of skeletal muscle weakness
-
Ptosis, diplopia, fatigable chewing, weak neck extensor muscles
- “Dropped head syndrome”
-
Ptosis, diplopia, fatigable chewing, weak neck extensor muscles
- Symptoms are worse later in the day and with exercise
- Fluctuating symptoms of skeletal muscle weakness
- Diagnosis
-
Tensilon test = IV endrophonium chloride (Tensilon)
- Reversible acetylcholinesterase inhibitor
- Eyelinds will open
-
Serum anti-AChR Abs
- Mostly in patients with generalized MG
-
MuSK Abs
- Mostly in patients with ocular MG
-
Repetitive nerve stimulation EMG
- Decremental response to repetitive stimulation
-
Single-fiber EMG
- Most sensitive test
- Increased “jitter”
-
Tensilon test = IV endrophonium chloride (Tensilon)
- __Treatment
- Pyridostigmine (Mestinon) = reversible cholinesterase inhibitor
- Steroids, azathioprine
- Complications
-
Myasthenic crisis = respiratory insufficiency
- Medical emergency requiring intubation
-
Myasthenic crisis = respiratory insufficiency
- Screening
- Patients should be screened for thymoma
- Thymectomy for patients age 18-55
A patient presents with 6-week history of generalized weakness. She says that the weakness slightly improves with exercise. She denies any visual symptoms.
- What is her most likely diagnosis?
- What is the pathogenesis?
- EMG with repetitive stimulation will show…
- She most likely has malignancy of the…
- Lambert-Eaton myasthenic syndrome (LEMS)
- Autoantibodies to presynaptic calcium channels
- Incremental response to repetitive stimulation
-
Lungs
- Small cell carcinomas
- Treatment of tumor can improve the weakness
- Small cell carcinomas
A 23 year-old man complains of progressive weakness over the past few days. His symptoms started in his feet and progressed up to his legs such that he has trouble walking. He is quite weak on exam, without reflexes, though his sensory exam in normal.
- You suspect he has…
- You perform a lumbar puncture on this patient. What do you expect to see?
- Infection with what agent commonly precedes the diagnosis?
- What is the best treatment?
- You perform nerve conduction studies on your patient. Which of the following findings is most suggestive of a demyelinating process?
- Guillain-Barre syndrome (GBS)
- High protein, normal WBC, normal RBC
- Campylobacter jejuni
- IVIG
- Conduction block and decreased conduction velocity
Guillain-Barre syndrome
- An autoimmune disorder characterized by demyelination, often following a GI illness
- Signs and symptoms
- Ascending weakness with minimal sensory symptoms
- Hyporeflexia
- Autonomic dysfunction = BP changes, arrhythmias
- Diagnosis
-
CSF
-
Albuminocytologic dissociation
- High protein, normal WBC
-
Albuminocytologic dissociation
-
Repetitive nerve stimulation EMG
- Incremental response to repetitive stimulation
-
CSF
- Treatment
-
IVIG or plasmapharesis
- Steroids have NO ROLE
- Supportive care = monitor respiration, PT/OT, pain control, psych support, DVT ppx, bowel/bladder care
-
IVIG or plasmapharesis
A patient complains of numbness of his hand that has been worsening over the past 6 months. The numbness is primarily on the pinky and ring finger and the patient cannot make a tight fist. You suspect an injury to the…
Ulnar nerve
- The course of the ulnar nerve around the posterior aspect of the medial epicondyle makes it susceptible to traumatic injury when patients strike the medial epicondyle
- This often causes parasthesiae in the 4th and 5th digits or more seriously, can cause “claw hand”
An intoxicated patient falls asleep with his arm slung over the back of his chair. When he awakens, he cannot extend his wrist and he has numbness on the back of his hand. You suspect an injury of the…
Radial nerve
- Can also be seen in injuries to the humerus
A 60 year old secretary presents to her primary care physician complaining of pain and tingling sensations in her first 3 digits (thumb, index and middle fingers). She has noticed that this pain often wakes her from sleep. On exam the physician notices that she also has loss in sensation on the lateral half of her ring finger. Lastly, there is atrophy of the thenar muscles.
- Where is the lesion most likely located?
- What does the patient have?
- Wrist
-
Carpal tunnel syndrome
- Caused by compression of the median nerve in the wrist
- Median nerve is comprised of the lateral and medial cords of the brachial plexus (C6 - T1 roots)
- Symptoms
-
Pain and paresthesia in digits 1-3 + lateral 4th digit
- Tinel’s test = pain by gently banging on the wrist
- Phalen’s test = pain by prolonged wrist flexion
- Thenar eminence atrophy
-
Pain and paresthesia in digits 1-3 + lateral 4th digit
- Screening
- Pregnancy, endocrinopathies, diabetes, thyroid, GH (acromegaly)
- Diagnosis
- EMG and NCS
- Treatment
- Splints at night, avoid repetitive movements
- Release of transverse carpal ligament
- Caused by compression of the median nerve in the wrist
A patient cannot extend his leg at the knee. This corresponds to an injury of which nerve?
Femoral nerve
- Weakness of knee extension and hip flexion
- Sensory loss over medial thigh, medial shin, arch of the foot
An obese man complains of burning on his right thigh. You suspect entrapment of which nerve…
Lateral femoral cutaneous
-
Meralgia paresthetic = lateral femoral cutaneous nerve syndrome
- Occurs with compression of nerve as it exits the inguinal ligament
- Sensory symptoms of lateral thigh
- Treatment
- Weight loss + looser clothes
Foot drop is characterized by steppage gait. While walking, people suffering the condition drag their toes along the ground or bend their knees to lift their foot higher than usual to avoid the dragging. Diseases that can cause foot drop include ALS, MS, or PD. Which nerve, when injured leads to foot drop?
Peroneal nerve
- Common peroneal nerve divides into deep and superficial branches
- Deep branch is responsible for foot drop + numbess of lateral calf and foot
- Can be seen in patients who fall asleep with their legs crossed
Tibial nerve
- Foot plantar flexion
Sciatic nerve
- Hamstring muscles
- Knee flexion
A patient falls while riding a bike a soon thereafter complains of a shooting pain from her neck down to her thumb. On exam, there is decreased sensation of her thumb as well as a decreased biceps reflex and weakness of the biceps muscle. You suspect an injury of the…
C6 nerve root
- Radiculopathy = nerve root injury!
Reflexes
- Biceps = C5, C6
- Brachioradialis = C5, C6
- Triceps = C6, C7
- Knee = L3, L4
- Ankle = S1, S2
Alcohol and diabetes are the most common reasons for “stocking- glove” peripheral neuropathy In the USA. What malignancy must be screened for in patients without an obvious cause for their symptoms?
Multiple myeloma
A patient presents with descending paralysis, an atypical pattern for most diseases. Based on the pattern of his symptoms, what is the most likely diagnosis?
Botulism
Ascending paralysis
- Guillain-Barre syndrome
- Transverse myelitis
- Tick paralysis
- Spinal cord compression
Descening paralysis
- Botulism
Parents of a 4 year-old boy have begun to notice that he is having difficulty walking. He used to run around and play all day, but recently it seems as though he’s been having trouble getting himself from a seated to standing position, and he fatigues easily. His parents take him to see the doctor, who does the appropriate work-up and unfortunately has to tell these loving parents that their child suffers from the heritable condition Duchenne Muscular Dystrophy (DMD). The parents are confused – “our baby’s muscles don’t look weak, look how big his calf muscles are!”.
- To this statement, the doctor must reply…
- The gene encoding which protein is mutated in this child?
- What is the mechanism of inheritance?
- This is a phenomenon called “pseudohypertrophy” – his muscles are actually infiltrating with fatty tissue as the muscles are breaking down.
- Dystrophin
- X-linked recessive
Muscular dystrophy
- A congenital muscle disorder caused by mutation of the dystrophin gene
- Dystrophin connects the cytoskeleton of a muscle fiber to the surrounding extracellular matrix
- This strengthens muscle fibers and allows them to relax and contract
- Only affects males
- Signs and symptoms
- Trouble walking at age 3-5, wheelchair bound at age 13, death in mid 20s
- Calf hypertrophy, dilated cardiomyopathy, mild mental retardation
- High CK levels
- Treatment
- Avoid exercise (injures muscles)
- Weekly steroids
-
Becker’s musclular dystrophy
- Milder version of DMD and patients can walk into early adulthood
- “Becker’s = better”
A 73 year-old with multiple medical problems presents with a 2 month history of muscle aches and pains. Serum CK is slightly elevated. What medication did he just start?
Atorvastatin
- Statins can cause myopathies
- Chronic steroid use can produce slowly progressive proximal myopathy
A 60 year-old man develops weakness in his distal muscles. The weakness is not symmetrical and one of his biceps is much weaker than the other. His legs are also not involved symmetrically. His CK is modestly elevated. He progresses to needing a cane, then walker, then wheelchair within 7 years. He has…
Inclusion body myositis
- Age > 50
- Signs and symptoms
- Asymmetric distal muscle weakness of hands and feet
- CK normal or slightly elevated
Polymyositis
- Age > 18
- Signs and symptoms
- Progressive in a “limb-girdle” distribution
- Cardiac involvement
- CK 50x higher
- Treatment
- Oral steroids, azathioprine, methotrexate, or IVIG
A 16 year-old patient with a history of progressive proximal muscle weakness underwent a muscle biopsy, which showed ragged red fibers. These histopathologic changes are consistent with which diagnosis?
Mitochondrial myopathy
- Biopsy
- Muscle tissue demonstrates “ragged red” muscle fibers
- Abnormal accumulation of mitochondria
- Muscle tissue demonstrates “ragged red” muscle fibers
- CSF
- High lactate and pyruvate
