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< Presentation of Case
>
A 32-year-old man, previously
healthy, presented to the emergency department (ED) in the
early morning with paralysis of four extremities. One week
earlier, he started to experience pain of the bilateral
shoulders and hips and progressive limb weakness. The weakness
was more obvious at the proximal part than the distal part of
the limbs. He denied use of diuretics, laxatives or big meals
recently. He became total paralysis this morning and couldn't
get off bed. He was sent to ED by ambulance. At ED,
quadriparesis with muscle power around 2-3 out of 5 was noted.
On physical
examination, the heart rate was 123 beats per minute and blood
pressure was 120/77 mmHg. The respirations were smooth and
around 18 breaths per minute, and the oxygen saturation while
the patient was breathing ambient air was 99%. His
consciousness was clear and his skin turgor was good with
moistened oral mucosa. There was no jugular venous distension,
goiter or lymphadenopathy. Cardiac examination revealed
tachycardia without murmurs. Examination of the lungs and
abdomen were unremarkable. There were no deformities or edema
of the extremities and distal pulses were present and equal
bilaterally. Neurologic examination revealed flaccid paralysis
of all extremities which involved the proximal and distal
muscles with the proximal muscles being worse. Sensory
function was intact but deep tendon reflexes were slightly
diminished. Cranial nerve function was grossly intact. The
laboratory tests on arrival at ED disclosed a serum potassium
level of 1.5 meq/L (reference value, 3.5–5 meq/L) and a
creatine kinase (CK) level of 671 IU/L (reference value,
38-174 IU/L) (table1
).
One day after initiation of intravenous
potassium replacement, the serum potassium level returned to
3.5 meq/L and the patient's muscle power recovered nearly
completely. Transtubular potassium gradient (TTKG) was not
high (TTKG= 2.5) [Note 1]. Hand tremor and palpitation were
noted during the hospitalization. Thyroid function was checked
and revealed a thyroid stimulating hormone (TSH) level of
0.013 IU/mL (reference value, 0.35–5.5 IU/mL) and a thyroxine
level (free T4) of 4.51 ng/dL (reference value, 0.89–1.80
ng/dL). Thyroid sonography demonstrated a hypoechoic and
heterogeneous echotexture[Note 2]. The anti-microsomal
antibody and anti-thyroglobulin antibody level was 2031.0 u/ml
(reference value, < 60 u/ml) and 45 (reference value,
<60 u/ml), respectively.
A diagnosis of hypokalemic
periodic paralysis associated with hyperthyroidism was made
and methimazole and beta-blocker (propranolol) were applied.
No more episodes of hypokalemia or paralysis recurred during
the follow-up as an outpatient.
[Note 1]: Hypokalemia
from extrarenal causes results in renal
potassium conservation and a TTKG less than 3. A higher
value suggests renal potassium losses.
[Note 2]: Reduced thyroid echogenicity
detected by thyroid ultrasonography is a strong predictor of
autoimmune thyroid disease even when these disorders have not
been suspected clinically. The ultrasonographic appearance of
both Graves' disease and Hashimoto thyroiditis are hypoechoic
and heterogeneous echotexture. ( ref : R. Schiefer and D. Dean(2008). Thyroid ultrasound and
ultrasound-guided FNA,2nd
ed, Springer, 2008, p63-75.
<
Lab data >
Hemogram
| |
WBC |
Hb |
Hct |
PLT |
Seg |
Baso |
Lym |
mono |
|
|
/μL |
g/dL |
% |
K/uL |
% |
% |
% |
% |
|
2009/5/21 |
11990 |
12.8 |
38.6 |
265 |
80 |
0.2 |
13.8 |
6.0 |
Biochemistry
| |
BUN |
Cre |
Na |
K |
Cl |
Ca |
Mg |
P |
|
|
mg/dl |
mg/dl |
mmol/l |
mmol/l |
mmol/l |
mmol/l |
mmol/l |
mg/dl |
|
2009/5/21 |
14 |
0.6 |
137 |
1.5 |
104 |
8.8 |
1.6 |
2.7 |
|
2009/5/22 |
|
|
|
3.5 |
|
|
|
|
|
2009/5/23 |
|
|
|
4.2 |
|
|
|
|
Biochemistry
| |
GOT |
Glu (PC) |
Uric acid |
CK |
CKMB |
Osmo |
|
|
U/L |
mg/dl |
mg/dl |
IU/L |
IU/L |
mOsm/L |
|
2009/5/21 |
20 |
143 |
5.7 |
671 |
13 |
282 |
Urine Biochemistry
|
|
Na |
K |
Cl |
Ca |
Creatinine |
Osmo |
|
2009 |
mmol/l |
mmol/l |
mmol/l |
mmol/l |
mg/dl |
mOsm/L |
|
98/5/22 |
47 |
3.5 |
58 |
7.0 |
29.6 |
264 |
Arterial blood
gas
| |
PH |
PCO2 |
PO2 |
HCO3 |
BE |
| 2009/5/21 |
7.40 |
35 |
94 |
21.7 |
-2.6 |
| 項 目 |
檢驗值(正常值) |
|
| Free T4 |
4.15 ng/dl |
(0.89-1.80) |
| TSH |
0.013 μIU/ml |
(0.35-5.5) |
| Anti-microsomal antibody |
2031 |
( <60 u/ml) |
| Anti-thyroglobuline antibody |
45 |
( <60
u/ml) |
< 病例分析
>
低鉀性麻痺（Hypokalemic
paralysis）是一種罕見且可能威脅生命的狀況。診斷上須從低血鉀著手，造成低血鉀的原因主要區分成兩大類，一是體內鉀離子缺乏(body
potassium deficit)，另一種是暫時性的鉀離子移入細胞(transcellular potassium
shift)。體內鉀離子缺乏又區分成經腎臟流失(renal loss)或非經腎臟流失(non-renal
loss)；經腎臟流失其TTKG> 3，或尿中鉀與肌酸酐比值>2.5（urine K+
/Creatinine>2.5mmol/mmol），其病因包括︰利尿劑的使用、第一型及第二型腎小管酸血症(renal tubular
acidosis)、原發性皮質醛酮過多症( primary aldosteronism)、Gitelman's
syndrome、Bartter's
syndrome等疾病。利尿劑的使用及腎小管酸血症會呈現代謝性酸血症；原發性皮質醛酮過多症、Gitelman's
syndrome與Bartter's syndrome則呈現代謝性鹼血症；原發性皮質醛酮過多症會高血壓，但Gitelman's
syndrome與Bartter's syndrome不會高血壓。另一方面，因暫時性的鉀離子移入細胞造成低血鉀其TTKG<
3或尿中鉀與肌酸酐比值<2.5（urine K+
/Creatinine
<2.5mmol/mmol），其病因包括︰甲狀腺週期性肌無力症、家族性週期性肌無力症(familial
peroidic paralysis)、陣發性週期性肌無力症(sporadic peroidic
paralysis)。
甲狀腺毒性週期性麻痺症(Thyrotoxic peroidic
paralysis，TPP)發生在甲狀腺機能亢進的病人身上，以低血鉀症及突發性肌肉無力為主要表現，好發於東方人，在甲狀腺機能亢進的亞洲人發生率約為2%左右，在北美的發生率約0.1-0.2
%，而好發年齡是20~40歲。一般而言，甲狀腺功能亢進好發於女性，但TPP好發於男性，發生率男女比，不同的研究報告顯示從17:1至70:1不等。
甲狀腺毒性週期性麻痺症的症狀，包括︰全身或局部性肌肉無力，肌肉無力一般影響近端肌肉(如上臂，大腿)比遠端肌肉厲害，影響下肢多於上肢，肌肉無力之發作時間可由數小時至數天；發作時，深部肌腱反射減低或消失，可以反覆的發作。甲狀腺毒性週期性麻痺症的病人只有在甲狀腺機能異常時才會發生，如果病人甲狀腺機能可控制在正常範圍內，則不會發病；而且要特別注意，一旦病人若處於甲狀腺機能亢進時，該病症很容易在高糖分飲食、喝酒及激烈運動後誘發。
甲狀腺機能亢進的原因在甲狀腺毒性週期性麻痺症的病人之中，仍然是以葛瑞芙茲氏病
( Graves' disease )
佔第一位。甲狀腺亢進相關之週期性肌無力症造成的低血鉀是暫時性的鉀離子移入細胞。理論上，甲狀腺素會增加鈉鉀幫浦（Na+/K+-ATPase）的活性，從而增加了鉀離子轉移進入肌肉細胞和紅血球細胞，低鉀血症是因鉀轉移到細胞內所致，鉀並沒有大量由腎臟中流失，體內實際鉀離子總含量也不缺乏,
TTKG或尿中鉀與肌酸酐比值（urine K+ /
Creatinine）是正常的。
因為甲狀腺毒性週期性麻痺症的重要致病機轉為甲狀腺機能亢進及低血鉀症，所以在治療上應給予抗甲狀腺藥物(如methimazole或
propylthiouracil ) 及
propranolol來使其甲狀腺機能恢復至正常；也可以使用手術或放射性碘131來治療，並且適當補充鉀離子，以改善其肢體麻痺的症狀及減少心律不整的發生。
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Case Discussion
繼續教育考題