From the Editors

NephroQuiz: muscles and bananas.

NephroQuiz is curated by BMC Nephrology Editorial Board Members from Johns Hopkins University, Dr. Hanouneh and Dr. Cervantes. It aims to engage readers with clinical vignettes and problem solving. The USMLE-style questions are designed to test knowledge and engage with published literature.
Mikhail Sinelnikov Oct 08, 2024

A 40-year-old African American man arrived at the emergency room experiencing profound muscle weakness. Past medical history revealed sporadic muscle tightness occurring 1-3 times per week, alleviated by consuming bananas. He was not using any medications, and his family history was noteworthy for hyperthyroidism and episodes of hypokalemia in his brother and mother.

Upon presentation, vital signs were temperature 98.4°F, blood pressure 127/83 mmHg, heart rate 111 beats/minute, respiratory rate 11 breaths/ minute, and oxygen saturation 96% on room air. Physical examination revealed pronounced weakness in both upper and lower extremities (strength assessed at 0/5) with areflexia.

Laboratory results are shown in Table 1. The electrocardiogram demonstrated sinus tachycardia with prolonged QTc interval of 606 ms. Swift replacement of hypokalemia effectively alleviated his symptoms, albeit leading to transient hyperkalemia that spontaneously resolved.

 Table 1. Basic Laboratory Tests. 

Tests​

Results​

Normal range​

Sodium​

139 mmol/L​

132-148 mmol/L​

Potassium​

<1.5 mmol/L​

3.5-5 mmol/L​

Chloride​

105 mmol/L​

98-111 mmol/L​

Bicarbonate​

21 mmol/L​

23-32 mmol/L​

Blood Urea Nitrogen​

18 mg/dL​

10-25 mg/dL​

Creatinine​

0.91 mg/dL​

0.7-1.4 mg/dL​

Calcium ​

9.3 mg/dL​

8.4-10.5 mg/dL​

Albumin​

3.9 g/dL​

3.5-5.0 g/dL​

Total protein​

7.2 g/dL ​

6.6-8.7 g/dL​

Glucose​

90 mg/dL​

65-100 mg/dL​

Magnesium ​

1.9 mg/dL​

1.6-2.6 mg/dL​

Phosphorus ​

2.1 mg/dL​

2.5-4.5 mg/dL ​

AST​

64 U/L​

5-40 U/L​

ALT​

153 U/L​

5-41​

Bilirubin- total ​

0.3 mg/dL ​

0.2-1.2 mg/dL​

Alkaline phosphatase ​

79 U/L​

40-129 U/L​

Random urine K/Cr ratio​

10.7 mmol/g Cr​

17-121 mmol/g Cr​

TSH​

< 0.006 mcIU/mL​

0.270-4.200 mcIU/mL​

Free T3​

13.0 pg/mL​

2.1-4.4 pg/mL​

Free T4 ​

3.04 ng/dL​

0.9-1.70 ng/dL​

Thyroid Stimulating Ig (TSI)​

3.43 IU/L​

<=0.54 IU/L​

Thyroid Peroxidase Ab ​

62.6 IU/mL​

0.0-9.0 IU/mL​

The correct answer, link to published case and explanation will be provided in the comment section. 

Click here to read the original case report, published in BMC Nephrology. We encourage discussion of the case and questions in the comments.