Approach to Inborn Errors of Metabolism


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Approach to Inborn Errors of Metabolism
Andrew M. Ellefson MD Cpt, USA, MC
Pgy-2 NCC Pediatrics

Goals for this lecture:
 Discuss acute/emergency management of IEMs.  Review broad categories of IEMs.  Focus on Board favorite zebras.  Complete the Board prep. Objectives in most
recent 2006 edition.  Integrate the “Laughing your way through Boards”
tips.  Have fun with this usually stressful topic.

What we WON’T DO:
 Memorize metabolic pathways.  Mention, think of, or utter the enzyme α-
ketoglutarate dehydrogenase complex.  Laugh at, throw bagels or coffee at, or otherwise mock Drew.  Discuss the adverse sequelae of the Eagle’s previous decision to recruit T.O.

IEM Board/Prep Goals:

 Recognize
– Urea Cycle defects – Organic acidemias – S+S of CHO disorders – S+S of Galactosemia – S+S of hyperinsulinism – Glycogen Storage Dz – Lipoprotein Disorders – Gaucher + Lipid Storage Dz – S+S of Tay-Sachs – S+S of Fatty Acid and
Carnitine metabolism

 Inheritance patterns  Indication for genetics  Eval of hypoglycemia  Eval of acidosis  Vitamin Rx for enzyme
disorders  Treat Hypoglycemia  Natural Hx of PKU  Plan/diet for PKU  Manage Glycogen storage
diseases- Type 1

IEM- Index of Suspicion:
 Rapid deterioration in an otherwise well infant.  Septic appearing infant or abnl sepsis such as
E.coli.  Failure to thrive.  Regression in milestones.  Recurrent emesis or feeding difficulty, alterations
in respirations, abnl urine/body smell, changing MS/lethargy, jaundice, sz, intractable hiccups.  Can masquerade like pyloric stenosis.  Dietary aversion- proteins, carbs.

Basic Principles:
 Although individually rare, altogether they are 1:800-5000 incidence.
 Broadly Defined: An inherent deficiency in a key metabolic pathway resulting in
– Cellular Intoxication – Energy deprivation – Mixture of the two

History and Antecedent Events:
 Catabolic state induction
(sepsis,fasting,dehydration)
 Protein intake  Change or addition of PO proteins, carbs,
etc… in formula  **Gotta ask- Consanguinity  FHx of SIDS

Assessment:

 Detailed H+P
– Describe sz – Fevers
-Milestones -FHx -Mom’s GsPs -NAT questions

 **Dysmorphology does not r/o IEMs**
 Physical Exam:
– Vitals – Level of alertness – Abnl activity/mvmts – CV- perfusion – Dysmorphology, hair,
smell, eyes-cornea – Abdo- HS megaly – Neuro- DTRs, tone, etc – Skin- bruise, pigment,
color

Emergency Management:

 Can be life threatening event requiring rapid assessment and management.
 ABC’s

 ABG-acidosis
 BMP, Ca and LFTs
 NH4
 Lactate, Pyruvate
 CBC, Blood Cx if uncertain
 Coags- PT/PTT
 UA-ketones, urine reducing substances, hold for OA/AAs
 Newborn scrn results
 LP- r/o Meningitis, but send lactate STAT, AAs, hold tubes for future
 Drug tox screen if indicated.
 **Hold spun blood or urine sample in fridge for later if possbile.
– **ABG, Lactate are iced STAT samples
– ** NH4 should be free flowing, arterial sample

Emergency Management:

 Correct hypotension.
 NPO, reverse catabolism with D5D10 1-1.5 x maint.
 Correct hypoglycemia.
 Correct metabolic acidosis.
 Dialysis, lactulose if High/toxic NH4
– (nl is <35µmol/L)

 Search for and treat precipitants; ie: Infection, dehydration.
 Low threshold for Sepsis w/u + ABx if uncertain.
 Pyridoxine for neonatal sz. if AED no-response
 Ativan, Versed, AEDs for status epilepticus.

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Approach to Inborn Errors of Metabolism