In the latest in our monthly series, Dr James Chambers asked readers to suggest what was causing ongoing nausea and tingling fingers in a female patient. Answer revealed below!
You see a 64-year-old woman in your afternoon clinic. She tells you that she is sorry to bother you, but this awful nausea just isn’t going away. On probing deeper, you find she has been feeling nauseous daily for around 3 months now. It began as an occasional feeling when cooking or smelling food but quickly became more constant, although it has never made her vomit.
While her weight has remained stable up to now, the patient has noticed the nausea is affecting her appetite, and she is worried she will soon start to lose weight if nothing is done. She reports no problems swallowing and no pain in her stomach or changes in bowel habits. She has already tried altering her diet to include more plain foods and apart from complaints from her husband, it has made little difference.
The only other change the patient has noticed is some tingling in her fingers, which is often worse at night when she tries to sleep. Her neighbour told her it was probably just carpal tunnel syndrome, although the wrist splint she bought online doesn’t seem to be helping.
Looking at her notes, you notice she has a history of hypertension, diabetes and GORD. Her medications include amlodipine, metformin and omeprazole. You can see she very rarely comes to see you and is recorded as a non-smoker.
On examination, you record the following observations: heart rate 74; respiratory rate 16; BP 135/90; O2 Sats 99%; temperature 36.7 degrees.
You find that her chest sounds clear with normal heart sounds. Her abdomen feels soft and non-tender with normal bowel sounds. On neurological assessment her tone, power and reflexes are all normal. She has normal visual acuity and perception. You can’t find any objective sensory loss on examination either.
Unsure of the cause of her symptoms, you arrange for some routine blood tests which reveal the following: FBC normal; U&E normal; LFT normal; serum CRP normal; serum calcium 2.0 mmol/L ( reference 2.20-2.60); serum albumin 35 g/dl ( reference 35-50); serum ALP 120 U/L ( reference 30-130); serum PTH 8.07 pmol/L (reference 1.95-8.49); serum total 25-OH vitamin D 75 nmol/L (reference 50-150).
What blood test would you now consider?
Answer: Based on the finding of low serum calcium it would be appropriate to check serum magnesium levels. In this case, the result showed this patient’s serum magnesium was also low.
The mechanism for how magnesium affects calcium levels is not fully understood, but research suggests that hypomagnesia impairs the secretion of PTH, which in turn causes low calcium due to the role of PTH in calcium regulation. It is also thought to cause PTH resistance, which could explain why this patient’s PTH was at the upper end of normal.
There is also evidence that magnesium has a role in activating enzymes involved in vitamin D synthesis and metabolism. Vitamin D is important for absorption of calcium from the gut and the kidney. Hence it is thought impaired vitamin D synthesis can lead to calcium depletion.
It’s well known that both low magnesium and low calcium can cause nausea and tingling sensations, and it’s likely both factors contributed to this patient’s symptoms. However, if the magnesium is not corrected first, the calcium is unlikely to return to normal. In this case, I considered the likely cause of the low magnesium was her omeprazole, which had been started six months prior to our consultation. The exact mechanism for how PPIs cause hypomagnesemia remains unclear, but research suggests they play a role in altering its absorption through active transport channels in the intestine, either directly or by affecting the intestinal pH.
As the patient’s reflux was fairly mild, the medication was stopped and instead changed to PRN Gaviscon. Repeat bloods four weeks later showed normal magnesium, calcium and most importantly, all her symptoms resolved.
So – next time you see an unexplained low calcium, think 0Mg – could it be their magnesium?!
Dr James Chambers is a GP Registrar in Staffordshire
Pulse October survey
Take our April 2025 survey to potentially win £200 worth of tokens
