Diagnostic Evaluation of Intermittent Weakness - Flowchart

Diagnostic Evaluation of Intermittent Weakness - Flowchart

Diagnostic Evaluation of Intermittent Weakness - Flowchart

«Flowchart»

Intermittent weakness

Intermittent weakness

Intermittent weakness

Intermittent weakness

Exam usually normal between attacks
Proximal > distal weakness during attacks

Exam usually normal between attacks
Proximal > distal weakness during attacks

Exam usually normal between attacks
Proximal > distal weakness during attacks

Muscle biopsy

Muscle biopsy

Muscle biopsy

AChR or Musk AB positive

AChR or Musk AB positive

AChR or Musk AB positive

End

End

End

Myoglobinuria

Myoglobinuria

Myoglobinuria

Yes

Yes

Yes

No

No

No

Yes

Yes

Yes

No

No

No

Acquired seropositive
MG

Acquired seropositive
MG

Acquired seropositive
MG

Myotonia on exam

Myotonia on exam

Myotonia on exam

Yes

Yes

Yes

No

No

No

Normal or elevated potassium level

Normal or elevated potassium level

Normal or elevated potassium level

Hyperkalemic PP
Paramyotonia congenita

Hyperkalemic PP
Paramyotonia congenita

Hyperkalemic PP
Paramyotonia congenita

DNA test confirms diagnosis

DNA test confirms diagnosis

DNA test confirms diagnosis

Low potassium level

Low potassium level

Low potassium level

Hypokalemic PP

Hypokalemic PP

Hypokalemic PP

AChR AB, acetylcholine receptor antibody; CPT, carnitine palmitoyltransferase; EOMs, extraocular muscles; MG, myasthenia gravis; PP, periodic paralysis.

AChR AB, acetylcholine receptor antibody; CPT, carnitine palmitoyltransferase; EOMs, extraocular muscles; MG, myasthenia gravis; PP, periodic paralysis.

AChR AB, acetylcholine receptor antibody; CPT, carnitine palmitoyltransferase; EOMs, extraocular muscles; MG, myasthenia gravis; PP, periodic paralysis.

^* Genetic testing

^* Genetic testing

^* Genetic testing

^*

^** If Abs, RNS, SFEMG are all normal or negative

^** If Abs, RNS, SFEMG are all normal or negative

^** If Abs, RNS, SFEMG are all normal or negative

^**

Genetic testing

Genetic testing

Genetic testing

No diagnosis

No diagnosis

No diagnosis

Forearm exercise

Forearm exercise

Forearm exercise

Reduced lactic acid rise
Consider glycolytic defect

Reduced lactic acid rise
Consider glycolytic defect

Reduced

Normal lactic acid rise
Consider CPT deficiency or other fatty acid metabolism disorders

Normal lactic acid rise
Consider CPT deficiency or other fatty acid metabolism disorders

Normal

Check chest CT for thymoma

Check chest CT for thymoma

Check chest CT for thymoma

Lambert-Eaton myasthenic syndrome

Lambert-Eaton myasthenic syndrome

Lambert-Eaton myasthenic syndrome

Consider:
Seronegative MG
Congenital myasthenia^*
Psychosomatic weakness^**

Consider:
Seronegative MG
Congenital myasthenia^*
Psychosomatic weakness^**

Consider:
Seronegative MG
Congenital myasthenia^*
Psychosomatic weakness^**

^* *
^** ^**

Decrement on 2-3 Hz repetitive nerve stimulation (RNS) or increased jitter on single fiber EMG (SFEMG)

Decrement on 2-3 Hz repetitive nerve stimulation (RNS) or increased jitter on single fiber EMG (SFEMG)

Decrement on 2-3 Hz repetitive nerve stimulation (RNS) or increased jitter on single fiber EMG (SFEMG)

Yes

Yes

Yes

No

No

No

Check:
Voltage gated Ca channel Abs
Chest CT for lung Ca

Check:
Voltage gated Ca channel Abs
Chest CT for lung Ca

Check:
Voltage gated Ca channel Abs
Chest CT for lung Ca

Variable weakness includes EOMs, ptosis, bulbar and limb muscles

Variable weakness includes EOMs, ptosis, bulbar and limb muscles

Variable

Exam normal between attacks
Proximal > distal weakness during attacks

Exam normal between attacks
Proximal > distal weakness during attacks

Exam

Check for dysmorphic features
Genetic testing for
Anderson-Tawil syndrome

Check for dysmorphic features
Genetic testing for
Anderson-Tawil syndrome

Check for dysmorphic features
Genetic testing for
Anderson-Tawil syndrome

EKG

EKG

EKG

Abnormal

Abnormal

Abnormal

Normal

Normal

Normal