|Home | About | Journals | Submit | Contact Us | Français|
In Creutzfeldt—Jakob disease (CJD) routine biochemical tests are usually within normal limits. A few patients have had slight increases in liver enzymes and bilirubin, or persistent hypercalcaemia1. Hypokalaemia does not seem to have been reported.
A man aged 79 was admitted after four weeks of progressive unsteadiness and intermittent diplopia. His only medication was nifedipine for hypertension. He was fully oriented and coherent, and examination of the nervous system revealed only mild incoordination of the left arm and hyporeflexia. Sensation was normal, there was no wasting, and fasciculation and myoclonus were absent. All haematological and biochemical tests were normal apart from a slightly depressed potassium (3.4 mmol/L). Subsequent examination of case notes indicated a similar plasma potassium a year previously, when the patient had a knee replacement. A brain MRI scan showed only age-related ischaemic changes.
Within two weeks from admission the patient became grossly ataxic and was intermittently confused; myoclonic jerks were observed. A neurologist raised the possibility of CJD and he was transferred to the regional neurology centre for the appropriate tests. The electroencephalogram was not typical of CJD, but cerebrospinal fluid was positive for the brain specific protein 14-3-3; also, S100b was high at 2.99 ng/mL (normal <0.38). Autoantibody screening, including ganglioside and cerebellum antibodies (Purkinje and neuronal), was negative. Genetic testing showed the patient to be valine homozygous at codon 129 of the prion protein gene with no apparent mutations; this rules out familial CJD.
The patient deteriorated to frank dementia and akinetic mutism within two months. Apart from the neurological deterioration, a striking feature was of progressive hypokalaemia, with potassium as low as 2.2 mmol/L despite oral supplements. This refractory hypokalaemia was complicated by several episodes of bowel pseudo-obstruction and of supraventricular tachycardia. There was no apparent cause such as intercurrent illness, drug therapy, vomiting or diarrhoea. Renal function, plasma sodium and plasma cortisol were all within normal limits, as was 24 h potassium excretion (64 mmol/L at a time when plasma sodium was 2.8 mmol/L). Aldosterone and renin studies were not performed. The patient died after three months and necropsy was not done.
Box 1 Diagnostic criteria for sporadic CJD (from Ref. 2)
This patient had features compatible with sporadic CJD (Box 1). The progressive worsening of hypokalaemia that accompanied his neurological deterioration raised the question whether CJD can affect potassium metabolism. This hypothesis is somewhat weakened by the presence of mild hypokalaemia a year before onset of symptoms. Clinically, the hypokalaemia and its effects were very hard to manage. The possible association with CJD deserves further exploration.
I thank Dr Fyaad Ahmed, Dr Andrea Loman and Professor RG Will for their help.