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A 32-year-old woman is 19 weeks pregnant
and presents to the emergency room with dysarthria
and vision changes. She has had two
previous hospitalizations during this pregnancy
for hyperemesis gravidarum treated with
intravenous fluids and anti-emetics. She has
lost 15 pounds since the start of her pregnancy.
She is on no medications and has no other significant
past medical history. On physical exam,
she is noted to have bilateral nystagmus and
gait ataxia. She has absent ankle jerks and decreased
sensation to temperature and pinprick
in her lower extremities. A CBC is checked and
is normal with normal MCV, Serum methylmalonic
acid levels are normal.
What laboratory test will confirm the
diagnosis?
A) Thiamine levels
B) No diagnostic testing needed, empiric therapy with niacin is warranted
C) Serum Cobalamin level
D) Serum zinc level
E) Serum copper level
What is A;This patient is suffering from thiamine deficiency and Wernicke’s encephalopathy. The classic triad of Wernicke’s encephalopathy consists of encephalopathy, oculomotor dysfunction and gait ataxia although peripheral neuropathy is common as is vestibular dysfunction without hearing loss. Wernicke’s encephalopathy is difficult to confirm although serum thiamine levels should be checked. The index of suspicion should be high in patients at risk for thiamine deficiency and IV administration of thiamine is safe and inexpensive as well as effective and should not be delayed as untreated Wernicke’s encephalopathy can progress to coma and death. Niacin deficiency is uncommon in developed countries although can be seen in individuals with alcoholism, anorexia nervosa or malabsorptive diseases. Niacin deficiency causes pellagra that is characterized by a symmetric hyperpigmented rash on sun exposed areas, diarrhea, red tongue, dementia, delusions and disorientation. Niacin deficiency is diagnosed by 24-hour urine tests for niacin metabolites although empiric treatment with niacin supplementation is usually the first course of action in a patient with typical symptoms. B12 deficiency is diagnosed by checking serum cobalamin level and confirming with methylmalonic acid and homocysteine levels. B12 deficiency causes anemia, macrocytic red cells with MCV >100, and neurologic symptoms. Serum methylmalonic acid and homocysteine levels are elevated in B12 deficiency. Although, this patient did have neurologic findings, the serum methylmalonic acid level was normal making the diagnosis of B12 deficiency less likely. Copper deficiency will cause a myelopathy although dietary copper deficiency is rare. Copper deficiency is commonly caused by gastric surgery but can also be seen with excessive zinc ingestion, malabsorption. The diagnosis is confirmed with decreased serum copper or ceruloplasmin level as >90% of circulating copper is bound to ceruloplasmin. Excessive zinc ingestion can cause copper deficiency as zinc and copper are competitively absorbed from the gastrointestinal tract. Zinc levels should be measured if the etiology of the copper deficiency is unknown.