Weakness is the inability to carry out a desired movement with normal force because of a reduction in strength of the muscles. Pts often confuse the states of malaise or listlessness, with true weakness. Fatigue is the diminution of strength with repetitive action
Paresis is partial or incomplete loss of contractility, while paralysis and plegia are complete. Quad is all four, para is lower limbs, hemi is one side, mono is one limb.
Myelopathy is a lesion of the spinal cord
Myopathy is a disease affecting muscle
A spinal nerve is the nerve exiting the anterior horn of the cord, while a peripheral nerve is a nerve outside of the spinal column.
Myotome refers to a group of muscles receiving innervation from the same segment of the spinal cord. Bulbar refers to the tongue, jaw, face and larynx.
Often unilateral and accompanied by deficits such as:
Aphasias, agnosias (lack of awareness of deficits), apraxias (inabilities to perform complex motor actions, ie. Button a shirt). Always must distinguish aphasias from dysarthrias, as the latter can be brainstem or cerebellar lesion.
Processes involving the brainstem or internal capsule can give weakness, basal ganglia can present as abnormal movements.
The line between central/peripheral or UMN/LMN is the exit of the spinal nerve from the anterior horn.
Airway and respiratory failure are the big killers. Circulatory collapse is also a possibility. Assess phonation and the ability to handle secretions. Tachypnea is an ominous sign (tidal volume usually disappears before upper airway collapse.) Pulse ox and PCO2 are poor indicators, for patients with GBS, MG, or other cause of rapid deterioration from weakness, obtain pulmonary function testing. FVC (forced vital capacity less 10-12 cc/kg or a NIF (negative inspiratory force) <20 cmH2O may indicate the need for mechanical ventilation. These results may be thrown off by the inability of the patient to make a tight seal around the pulm. function mouthpiece.
Probably wise to avoid Sux if intubation is needed, though the risk is probably not real until 72 hours post onset.
Autonomic dystability can accompany GBS, and is often heralded by sinus tach on ekg.
· Are cortical signs present (aphasia, agnosia, apraxia, or neglect)?
· Is the face involved?
· Is there a dermatomal or myotomal pattern to the weakness? Is the description of the weakness consistent with a peripheral nerve?
· Is there bowel or bladder involvement?
Unilateral facial weakness is either in the brainstem or the cortex. Localized process suggests peripheral nerve injury.
· Is mental status impaired?
· Which limbs are involved?
· Sensory involvement? Is there a level?
· Bladder involvement?
· Primary or Distal muscle groups?
· Flucuating pattern to the weakness?
· Are there associated bulbar signs?
CNS lesions will usually have a change in mental status unless in the spinal cord.
A sensory level and/or bladder involvement points towards a myelopathy. Proximal>distal weakness is often the sign of a myopathy. If the weakness has a fatiguing pattern, the deficit will usually be at the NMJ (neuromuscular junction.) Acute attacks of weakness that resolve in a few hours suggest periodic paralysis. Visual and bulbar involvement often indicates an NMJ problem. Consider occult infection or infant botulism at the extremes of age. Cold reversal is ciguatera poisoning.
Lhermittes sign: an electric or tingling sensation that travels down the spine and into the extremities is a common sign of MS, but can be seen with radiculopathies and vitamin B12 deficiency as well.
Look for the bronze discoloration of Addison’s disease or the heliotropic, violaceous rash of dermatomyositis. If anything in the history suggests tick exposure, search diligently, as removal can be curative of the weakness. A careful neck exam for thyroid involvement can also be revelatory.
Identify if UMN (spasticity, hyperreflexia, and extensor babinski) signs or LMN (hyporeflexia, fasiculations, hyporeflexia) signs. Initially, a UMN lesion can present with LMN signs, developing UMN later.
The key to differentiating GBS and other neuropathies from myopathies and NMJ disorders when presented with bilateral LMN signs is sensory involvement. GBS will have sensory involvement, myopathies should have no effect other than myalgia on the sensory system.
Rising out of a chair or stepping up on a chair is a good test for prox motor weakness.
Grade strength in the involved muscles using the standard scale:
1. Palpable or visible contraction
2. Active movement through ROM when gravity is eliminated
3. Active movement through ROM against gravity
4. Active movement through ROM through weak resistance
Cerebral hemisphere lesions should hace asymmetry between the sides with hyperreflexia on the affected side. If nerve root compression is suspected, the lack of a particular reflex can indicate the level. Extensor babinskis must have the other toes fan out as well.
Hoffman Sign: reflex flexion of the fingers and thumb. Elicit by holding the patients middle finger between your index and middle finger and flicking down on the distal phalanx with your thumb. If present, it is a sign of a UMN lesion.
Clonus: test with patient in supine position with the leg flexed at the knee. Rapidly dorsiflex the foot and hold it in dorsiflexion, if the foot jerks, clonus is present, another UMN sign
Cremasteric Reflex: (T12-L1) stroke thigh with tongue blade and see unilateral testicular rise
Anal Wink: (S2-S4) stroke skin around sphincter and see it contract. Absence is abnormal
Perform repetitive, sustained oculomotor testing
Shake forearm to observe tone of hand on wrist. For lower extremities have pt lie supine and relax their leg. Lift up the thigh, in normal patients the foot will initially lift off the bed and then settle and slide. In a flaccid pt, the foot will slide on the bed the entire way.
Spasticity selectively targets the flexors of the upper extremities and the extensors of the legs. Rigidity increases both flexors and extensors.
Lower motor neuron sign. Can be differed from benign fasciculations by the fact that they occur randomly over many parts of the muscle, while the benign form is usually in the same muscle fascicle.
Spasticity caused by UMN lesions will result in a stiff jerky gait while walking. LMN lesions will give a floppy foot that slaps as the patient walks.
Cortical lesions typically cause a slight loss of sensation effecting touch and proprioception more than pain. Stereognosis refers to identifying objects by touch. Graphesthesia is tested by tracing a number or letter in the patients palm.
Assessing Psychogenic Causes of Weakness
giveaway weakness, resistance then sudden loss is common in malingerers
Hoovers sign the test with lifting one leg while not pushing down on opposite heel
A arm that drifts down without pronating is fake
A paralyzed arm will swing back and forth if you shake a patients shoulders
Horners syndrome (ptosis, miosis, and anhidrosis) can be seen in internal carotid dissection, though anhidrosis wont be present in this causes as the sweat innervation comes from around external carotid
Central Unilateral Weakness
First ask whether the limbs and face on the same side are involved. Eyes will look towards the lesion if the frontal lobe is damaged. Contralateral homonomous hemianopia (losing right/left half of vision of both eyes) which can occur anywhere along the hemispheric visual pathway.
· Deep hypertensive hemorrhages or ischemic lacunar strokes can cause weakness without cortical signs.
· Pure Motor Stroke-paralysis of the face, arm and leg on one side s other signs will usually localize to the posterior limb of the internal capsule or the pons
· Ataxic Hemiparesis-weakness of the lower limb associated with dysmetria of the arm or leg on the same side usually will localize to the corona radiate and the anterior limb of the internal capsule
· Sensorimotor Stroke-hemiparesis or hemiplegia with ipsilateral sensory impairment will be in the thalamus and adjacent internal capsule
· Dysarthria (clumsy hand syndrome)-facial weakness, severe dysarthria, and dysphagia, with mild hand weakness and clumsiness found in the corona radiate and the anterior limb of the internal capsule.
Crossed findings. III and IV=midbrain. VI and VII=pons. IX-XII=medulla. Most likely due to vertebrobasilar circulation stroke.
· Weber-midbrain, ipsilateral 3rd nerve palsy and contralateral hemiparesis
· Millard-Gubler-pons, ipsilateral facial palsy, contralateral hemiparesis
· Fovilles-pons, ipsilateral facial paresis, abducens palsy, contralateral hemiparesis
Diseased condition of the spinal roots
Will almost always be in the cervical or lumbosacral distributions
Lesion of a nerve plexus is identified by found by the presence of motor and sensory deficit involving more than one nerve.
Peripheral Nerve Processes
Most often neurapraxias, a temporary insult to a nerve which resolves when compression is relieved. Median nerve entrapment is the most common, Tinels sign (percussion directly over the median nerve at wrist) is not useful. Phalens is also fairly useless. Hand elevation test is better. Simply have the patient raise their hands over their head until the symptoms reoccur, if in median nerve distribution, then you have your diagnosis. Steroids are probably better than NSAIDs.
Saturday Night palsy is from compression of the radial in the axilla or along the humerus. Loss of grip strength which is restored with passive wrist extension.
Peroneal nerve compression from crossed knees or the straps of high heels can cause foot drop.
Central Bilateral Weakness
Will usually present with diminished consciousness unless localized to spinal cord. A lesion in the intrahemespheric fissure is more likely than bilat symmetrical cortical lesions. A tiny lesion in the decussation of the pyramids (cruciate paralysis of Bell) can give bilateral upper extremity weakness with no involvement of the legs.
· Locked-in-pons, quadriparesis with paralysis of horizontal eye movements and everything else. Only vertical eye motions preserved. Must diagnose early as there is a chance of recovery if the basilar artery is recanalized within 12 hours.
Bilat extremity weakness and sensory deficits. Typically the legs are involved, though cervical pathology can give this in the arms. There may be bowel and bladder involvement. Acute disruptions suggest vascular cause, while more chronic symptoms can be inflammatory. The most important point in this disorder is to recognize it and then rule out epidural compression syndrome. If it is strongly suspected, call spine surgeon and give dexamethasone (10-100 mg IV).
Often heralded by paresthesias and vibratory sense is almost always lost
Heavy Metal Polyneuropathy
Not from bad music. Most notable is lead
Almost always proximal>distal effects. Usually only sensory is muscle aches.
Inflammatory myopathies causing progressive proximal muscle weakness. Can also progress to dysphagia and respiratory failure. There is no sensory loss or effect on reflexes. Mostly women are effected, dermatomyositis can also hit children. ESR and CPK will be elevated.
Most commonly associated with potassium, but any significant lytes disturbance can cause weakness.
Hyperkalemic Periodic Paralysis
Autosomal dominant. Precipitated by exercise or cold exposure. Hyperkalemia is often not present during attacks.
Hypokalemic Periodic Paralysis
Can be familial or Thyrotoxic. Weakness is often confined to the limbs, though facial or respiratory weakness can occur as well. Hyporeflexic during attacks. Sensory exam is objectively normal. Rhythm monitoring may show PVCs or other disturbances. Attacks usually last 3-4 hours. Administering potassium will attenuate the attack, but should be done cautiously as whole body potassium is not low in this disorder.
Usually occur during sleep or after exercise (?) Usually start during the second decade of life. Will not have onset after age 30, so think thyroid.
Often affects Asians with thyroid disease. Increases NaK ATPase causing influx of K into cells. Since pumps are also activated by insulin, heavy carb meals will also cause attacks. Better strategy than replacing potassium in these patients is to give propranolol 1mg IV q10 min x 3.
Can treat with low dose KCl (<10 meq an hour) which will hasten recovery but also increase risks of rebound hyper-K (The American Journal of Emergency Medicine 22(7):544-547)
Non-selective b-blockers can also be used
The differential diagnosis of a combination of hypokalemia, normal pH and sodium, limb weakness, and a periodic pattern after eating binges is thyrotoxic periodic paralysis (TPP), familial hypokalemic periodic paralysis (FPP), or sporadic periodic paralysis (SPP). All three usually present with a hypokalemic paralysis after ingestion of large amounts of salted or sweet foods. However, if it’s the first episode, other causes of hypokalemic paralysis must be considered. These include barium poisoning, toluene exposure, renal potassium wasting, mineralocorticoid excess (hormonal or licorice induced) and gastrointestinal losses. An excellent clinical algorithm is available in an article by Lin et al. (6).
Unfortunately, the symptoms of thyrotoxicosis are often not present at the initial presentation of TPP, so thyroid function studies may be necessary to make the diagnosis if it’s the first attack ( and ). It is helpful if the symptoms of hyperthyroidism were present before the attack, or if there is a clear family history suggestive of FPP (which can be sporadic but is usually inherited as an autosomal dominant trait, with much higher penetrance in men).
The emergency treatment of TPP, SPP, and FPP is initially the same. Usually the attack will resolve spontaneously without any intervention, so observing the patient with continuous cardiac monitoring, pulse oximetry, and frequent muscle strength checks is often adequate treatment (2). Decompensation leading to stridor and respiratory failure or cardiac dysrhythmia can occur suddenly, so close observation is mandatory.
Because the cause of the hypokalemia is a shift of potassium into the muscle cells, there is usually no need to replace serum potassium unless the patient has these life-threatening symptoms. A tachycardia and elevated blood pressure are the most sensitive signs of TPP and increase the possibility of TPP over FPP or SPP (7). If TPP is the most likely diagnosis, propranolol, rather than potassium, is the treatment of choice ( and ). This avoids the danger of rebound hyperkalemia, which occurs in 3045% of TPP patients treated with potassium ( and ). Although there are no controlled studies demonstrating that potassium terminates the attack and there is no correlation between potassium dose and recovery time, potassium is usually administered if there is severe weakness, dysrhythmia, stridor, or respiratory failure ( and ).
If potassium treatment is necessary, it is preferable to administer the potassium orally as KCl at .2.4 mmol/kg every half-hour while following the EKG, serum potassium, and muscle strength (2). If potassium must be administered intravenously due to vomiting or inability to swallow, KCl can be administered in small boluses of .1 mmol/kg while monitoring the EKG continuously. Because sodium or dextrose infusions can reduce the serum potassium in these patients, D5 and saline solutions should be avoided. Mannitol is the preferred vehicle if a dilute infusion of KCl (2040 mml/L) is the elected therapy (2). Great care must be exercised because rebound hyperkalemia can occur as the attack subsides and the potassium returns to the serum from the muscle cells.
Repeated episodes of FPP, SPP, or TPP can result in serious interattack muscle weakness that is permanent, so long-term follow-up is necessary. An elevated creatine kinase reflects the ongoing muscle damage and pain that occurs in some patients with periodic paralysis (,  and ). It has been shown that hypokalemia can cause rhabdomyolysis and that may well be the mechanism for the myopathy ( and ).
Preventing further episodes can be as simple as avoiding high sodium, high carbohydrate meals, or it may require treatment with the carbonic anhydrase inhibitors acetazolamide (1251000 mg/day in divided doses) or dichlorphenamide (50200 mg/day). Because serious mental status changes can occur with these drugs, and acetazolamide may actually make the attacks worse in some patients, triamterene (25100 mg/day) or spironolactone (25100 mg/day) may be used instead (13).
1 R. Stedwell, K. Allen and L. Binder, Hypokalemic paralyses: a review of the etiologies, pathophysiology, presentation, and therapy, Am J Emerg Med 10 (1992), pp. 143148. Article | PDF (841 K) | View Record in Scopus | Cited By in Scopus (72)
2 R.H. Brown and J.R. Mendell, Muscular dystrophies and other muscle diseases. In: E. Braunwald, S.L. Hauser, A.S. Fauci, D.L. Longo, D.L. Kasper and J.L. Jameson, Editors, Harrison’s online, McGraw-Hill, New York (2001), p. 50.
3 V. Sansone, T. Links, G. Meola and M.R. Rose, Treatment for periodic paralysis (Protocol), Cochrane Database Syst Rev(2004) 3.
4 A. Chan, R. Shinde and C.C. Chow et al., Hyperinsulinaemia and Na+, K+-ATPase activity in thyrotoxic periodic paralysis, Clin Endocrinol 41 (1994), pp. 213216. Full Text via CrossRef | View Record in Scopus | Cited By in Scopus (43)
5 P.K. Ober, Thyrotoxic periodic paralysis in the United States, report of 7 cases and review of the literature, Medicine 71(1992), pp. 109120.
6 S. Lin, J. Chiu, C. Hsu and T. Chau, A simple and rapid approach to hypokalemic paralysis, Am J Emerg Med 21 (2003), pp. 487491. Article | PDF (70 K) | View Record in Scopus | Cited By in Scopus (12)
Neuromuscular Junction Processes
Neuromuscular Weakeness in the ICU
Hypoventilation and Respiratory Muscle Dysfunction
decreased neuromuscular capacity
sedative overdose, hypothyroidism, metabolic alkalosis, semistarvation.
COPDers also can develop decreased respiratory drive
Respiratory muscle weakness
Myopathy of Critical Illness
respiratory muscle weakness can be caused by sepsis. disuse, metabolic/nutritional abnormalities,
myopathy can result from the prolonged use of NMBAs
muscle atrophy is quite common.
malnutrition, Hypomagnesemia can effect respiratory muscles
Critical Illness Polyneuropathy
muscle atrophy and difficulty in weaning from ventilator. Acute axonal injury which is demonstrable on EMG-NCV. Linked to SIRS and MOD. There is no treatment, but the sate is usually self-limited.
Best review (Crit Care Med 2006;34:2835)