EMCrit.org

Neuromuscular Disorders

Myasthenia Gravis

ACh receptor antibodies

Assoc c thymus disorders

Pathologic fatigability of muscles.

The most common presenting symptoms are ocular (Ptosis, diplopia).   If limb weakness is involved it is usually greatest in upper extremities.

Normal pupils, dtrs, and sensory exam.

Testing

Gaze Testing

Easiest is extended gaze testing.

Cold Testing

If there is ptosis or EOM abnormalities, can perform cold testing.  Cover eye c ice pack for 2 minutes and see if sx improve.

Tensilon/edrophonium  test

·        There are reports of false positives in cases of botulism, eaton-lambert, ALS, GBS, and Cavernous sinus lesions

·        Measure the distance from the upper to the lower eyelid in the most severely affected eye

·        intravenous test dose of 1 to 2 mg is given first.

·        If no adverse reaction is found, and the patient does not dramatically improve in 30 to 90 seconds, a second dose of 3 mg is given.

·          If there is still no response, a final dose of 5 mg is given for a total maximum dosage of 10 mg.

·        Potential bradycardia from edrophonium, atropine should be available at the bedside. Also, because of the potential cholinergic effect of increased airway secretions, this test should be used with caution in asthmatics and patients with COPD

Below from Jama 2005;293:1906-1914.

 
Box. Edrophonium Test

Establish reliable peripheral intravenous access

Prepare a syringe with 2 mg of atropine (available in 0.4-mg/mL or 1-mg/mL ampules) to have handy

Prepare 1 mL (10 mg) of edrophonium in a tuberculin syringe (edrophonium is available in a 10-mg/mL solution in a 1-mL ampule [10 mg] or in a 10-mL vial [total of 100 mg])

Inject 2 mg (0.2 mL) slowly over 15 seconds while observing for an objective improvement in target muscles

Improvement should occur within 30 seconds and disappear in 5 minutes; if no response and no significant adverse effects, administer the remaining edrophonium (8 mg [0.8 mL]) for a total dose of 10 mg

Atropine should be injected (0.5 or 1 mg) in case of clinically significant bradycardia, respiratory distress, or syncope*

*Routine administration of atropine simultaneously with edrophonium for the purpose of diagnostic testing for myasthenia gravis is not recommended. Bartley and Bullock29 recommend using a 3-way stopcock with the edrophonium-containing syringe attached to the direct port and the atropine-containing syringe attached to the side port, so that atropine may be quickly injected in case of severe adverse effects

 

Diagnostic Dilemma

In treated pts, you must differentiate between too little ACh from myasthenic crisis (undertreatment) or Cholinergic Crisis (Overtreatment)

Often physical exam can help with cholinergics giving gastric hyperactivity, sweating, and other signs similar to organophosphate toxicity.  Sometimes the safer strategy is to withdraw all cholinergic medicine, support patient’s respiratory status and allow the consultant to interpret the patient’s sx as cholinergic crisis can be superimposed on myasthenic crisis.

Assess Resp Status

Patients often look good until just before they require emergent intubation

 

An easy bedside assessment used to follow ventilatory status is to have the patient count from 1 to 25 with one breath. With sequential performance of this, a decline in respiratory function will be detected as the patient fails to count as high as before

Ask the patient to cough and observe the force generated

Bedside spirometry for NIF and FVC

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 pulmonary function mouthpiece.

Intubation

Need ~ 50% the dose of non-depol or

2.6 x the dose of succinylcholine

(Mt Sinai J of Med 2002;69(1):31

Management

anticholinesterase therapy:  pyridostigmine is the oral agent of choice, neostigmine can be used parenterally

immunosuppressive therapy:  prednisone 60-150 mg/day

thymectomy: 

plasmapheresis: 

Lambert-Eaton Myasthenic Syndrome

is a rare disorder often associated with small-cell carcinoma of the lung. Autoantibodies cause an inadequate release of ACh from nerve terminals, affecting both nicotinic and muscarinic receptors. With repeated stimulation the amount of ACh in the synaptic cleft increases, leading to an increase in strength, the opposite of that seen with MG. The classic syndrome includes weakness that increases with use of muscles, hyporeflexia, and autonomic dysregulation. Management primarily focuses on treating the underlying neoplastic disorder, although plasmapheresis and immunoglobulin G (IgG) have been reported to be useful.  This disease unlike MG will often spare EOM and may have autonomic dysfunction.

 

Botulism

Clostridium botulinum, spore forming anaerobic, gram positive bacilli

Can withstand boiling for hours

Toxin mediated.  Blocks ACh release at the NMJ.

12-36 hrs post-ingestion.

1st cranial nerves are effected (papillary dilation), then descending paralysis/weakness

 

Botulinum toxin-can be released as aerosol or spread by contaminated food.  The most toxic substance known.

Prevents presynaptic release of ACh, therefore anticholinergic toxidrome, i.e.. dry mouth, ileus, and urinary retention.

Sx 1-3 days after inhalation

Starts c Bulbar palsies then descending flaccid paralysis c intact sensation and decreased reflexes

Four Ds

·        Diplopia

·        Dysarthria

·        Dysphonia

·        Dysphagia

 

Differential-G. Barre, myasthenia, Eaton Lambert, tick paralysis, hypokalemia, CO, diphtheria, metal poisoning

Antitoxin and toxoid vaccine available in scant supply.  Will probably need to demonstrate LP and EMG to exclude other diagnoses.  Two antitoxins bivalent (AB)  and trivalent (ABE)

Surfaces can be decontaminated c .1% bleach

Not transmissible

 

Dry tongue and sore throat, ileus, urinary retention, double vision, dysarthria, hyporeflexia

Trend vital capacity to see impending resp failure.

Consider miller fisher variant of guillain barre, get LP if diagnosis is in question in botulism it will be normal

Antitoxin available from CDC

Notify CDC and other EDs

Infant botulism

honey and corn syrup, but not necessarily any food source

floppy baby

check stool for toxin

Wound botulism

Usually in IVDAs (black tar heroin)

± antitoxin, consult toxicologist

Wound debridement

PCN 10-20 million units IV/day

Adult Onset Infantile Botulism (Undetermined)

Similiar to infant botulism, seen in adults with reduced stomach acidity or reduced gut flora which allows intraluminal growth.

 

Tick Paralysis