Potassium disturbances as a cause of metabolic neuromyopathy

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Intensive Care Med (1987) 13:208-210

Intensive Care M e d i c i n e © Springer-Verlag 1987

Case reports Potassium disturbances as a cause of metabolic n e u r o m y o p a t h y C. Villabona, P. Rodriguez, J. Joven, P. Costa, J. Avila and M. Valdes Department of Medicine, Hospital de Bellvitge, Hospitalet del Llobregat, Barcelona, Spain Received: 15 June 1986; accepted: 9 October 1986

Abstract. We report two cases of ascending muscular weakness progressing to areflexic quadriplegia caused by severe derangement of potassium homeostasis. The first patient presented with a 17-alpha-hydroxylase deficiency and severe hypokalemia. The second case had primary adrenocortical deficiency (Addison's disease) and extreme hyperkalemia. Complete recovery ensued after correction of the metabolic disorder in both cases. The role of potassium in the pathophysiology of neuromuscular excitation is discussed. We conclude that when neuromyopathy is present, metabolic causes should be considered and the serum potassium determined. Key words: Hypokalemia - Hyperkalemia - 17-alpha-hydroxylase deficiency - Adrenocortical deficiency - Quadriplegia

Potassium is accumulated in cells by an energy-dependent process so that the intracellular concentration far exceeds the extracellular concentration. The resting membrane potential is the voltage difference a cell maintains across its membrane in the steady state and is determined mainly by the concentration gradient for potassium [1]. Although neuromuscular manifestations are common in alterations in serum potassium concentrations in either direction, the appearance of quadriplegia is considered exceedingly unusual [1]. We describe here two cases where flaccid areflexic quadriplegia was found in the presence of severe hypokalemia in a patient with 17-alpha-hydroxylase deficiency and extreme hyperkalemia in a patient with adrenocortical deficiency (Addison's disease).

Case 1

This patient was a 19-year-old woman who had an older sister previously diagnosed as suffering from 17-alpha-hydroxylase deficiency. She was well until some days before admission when a polyuria-polydipsia syndrome developed with generalized muscular weakness, difficulty in walking and later in holding up the head. On admission to our hospital, she presented with primary amenorrhea and apparent hypogonadism with no evidence of secondary sexual characteristics. Flaccid and areflexic paralysis was observed in the extremities and trunk muscles without a sensory deficit; the proximal muscles were more severely affected. There were no changes in cerebral function and the rest of physical examination was otherwise normal. The blood pressure was 150/105mmHg. The serum potassium was 1.3 mmol/1 whereas the urinary potassium was 62 mmol/1. The sodium concentration in serum and urine was 147 and 12 retool/1 respectively. The serum chloride was 80 mmol/1, the calcium 2.2mmol/1 and the phosphorus 1.1 mmol/1. A specimen of venous blood disclosed that the PCO 2 was 35 mmHg, H C O 3 33.8 mmol/1, and the pH 7.59. All other laboratory investigations were normal. An electrocardiogram revealed prolongation of the PR interval and QRS period, flattening of the T wave and the presence of elevated U waves. During the first 24 h, 310 mmol of potassium were given intravenously together with dexamethasone ( 2 m g / 6 h ) . Quadriplegia disappeared completely in 48 h. The hormonal evaluation is delineated in Table 1. Case 2

A 53-year-old woman who had a history of inadequately treated renal tuberculosis in her 20's, developed Addison's disease at the age of 40 years. This was

C. Villabona et al.: Potassium disturbances and metabolic neuromyopathy Table 1. Hormonal parameters in the two patients

Discussion

Parameters

Case 1

Case 2

Progesterone (ng/ml)

2.2 undetectable 21 20 25 1.5

6.6

45 445-

0.7 1.6

6.5 6.6

8 - 24 Rise exceeding 6 Ixg/dl over basal level 13- 80 35 - 135

17-OH-progesterone

(ng/ml) Estradiol (pg/ml) LH (mUI/ml) FSH (mUI/ml) 17-ketosteroids (mg/24 h) Cortisol (lxg/dl) Basal After stimulation with cosyntropin ACTH (pg/ml) (9 a.m.) Urinary free cortisol 0xg/24 h) 17-hydroxycorticoids (rag/24 h) Plasma renin activity (ng/ml/h) Aldosterone excretion (~tg/24 h)

180 46

-

209

Normal values 0.5 1.6 0.3- 1 440 11 1l 15

0.2

2.5

3 - 11

0.1

6.5

0.5-2.5

6

0.4

3 - 17

treated with prednisone (7.5 mg daily) for 2 years. She spontaneously discontinued her treatment without further symtomatology. Two weeks before admission she complained of anorexia, asthenia and progressive weakness affecting mainly the legs with difficulty in moving the arms. On admission, physical examination showed that her skin was diffusely pigmented especially in the cutaneous creases and areolas, with black patches on the mucous membranes. She had a flaccid and areflexic quadriplegia with inability to lift the head from the pillow. Bilateral facial palsy was also noted. Sensory examination showed no apparent deficit and her consciousness was preserved. The blood pressure was 100/70 mmHg. The urea nitrogen in serum was 21.8mmol/l, and in urine 13.8 mmol/1. The potassium in serum and urine was 10 and 23.6 mmol/1 respectively. The same serum sample revealed a cortisol concentration of 317nmol/1 (normal, without stress, 248 to 662nmot) when assayed the following day. Arterial blood was drawn with a PaO 2 of 126mmHg, PaCO 2 29.8mmHg, H C O 3 13 m m o l / l and pH 7.25. An electrocardiogram revealed widened QRS complexes and peaked T waves; P waves were not identifiable. The patient was treated with hydrocortisone, sodium bicarbonate, glucose plus insulin and isotonic sodium solution with progressive and evident benefit. The quadriplegia disappeared completely in 48 h. Hormonal results are shown in Table 1.

What is striking about these two cases is that these opposite situations produced the same neuromuscular manifestations, i.e. flaccid areflexic quadriplegia. Disorders in internal and external potassium balance were found in both cases. In case 1, the biochemical data suggested the presence of hypermineralcorticism. Steroid hormones with mineralcorticoid effects cause sodium retention, suppression of renin secretion, hypertension, metabolic alkalosis and hypokalemia. Flaccid quadriplegia, although rare, has been described when the plasma level of potassium falls below 2 mmol/1 [4]. To our knowledge, this is the first reported case related to 17-alpha-hydroxylase deficiency. This neuromuscular complication has also been described in Addison's disease [5]. In mild states of adrenocortical insufficiency the condition is well tolerated if adequate dietary sodium chloride is available. When there is impaired distal renal tubular transport, inadequate mineralcorticoid stimulation may result in urinary sodium wasting and retention of potassium and hydrogen ions, resulting in extracellular fluid volume contraction, hyperkalemia and metabolic acidosis. The mechanism by which hypo- and hyperkalemia interfere with neuromuscular transmission remains unclear. In the resting state, all nerve and muscle fibers are polarized with the interior of the cell negative to the outside surface, the so called resting transmembrane electrical potential (Em). In the resting condition, K ions tend to diffuse outward while Na ions tend to be driven into the cell, this ionic diffusion being limited by the very low permeability of the cell membrane to Na. When a stimulus temporarily reduces the E m (depolarization) to the thresold potential (Et) , an action potential results by the opening of channels which permit a rapid entry of Na into the cell. The arrival of the nerve action potential at the motor end plate initiates the muscular contraction. E m is closely related to the potassium concentration ratio existing across the sarcolemmal membrane. In terms of conductance, the muscle cell can be considered to function as a potassium electrode. However, the permeability of Na ions, although 100-fold lower than of potassium, remains significant, and a modification of the Nernst equation should be used to predict E m (Goldman) [2]:

E m = - 6 1 log Ki+0"01 Nai Ke+0.01 Na e The excitability of neuromuscular tissue is defined as the difference between E m and normal E t. Any fac-

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C. Villabona et al.: Potassium disturbances and metabolic neuromyopathy

tor which increases Ern or decreases E t will render the tissue less excitable while factors which decrease E m or increase E t will enhance excitability. Obviously, changes in K e will be more important than changes in the already high K i. When hypokalemia occurs, K i / K e is increased, E m is also increased, and then neuromuscular excitability will be decreased, leading to paralysis. When hyperkalemia is present, the situation is reversed. Hyperkalemia has two effects on this process; if hyperkalemia is moderate there is a reduction in the E m by diminishing the K i / K e and it will render the muscle hyperexcitable. However, when the hyperkalemia is profound, a second effect predominates consisting of the inactivation of sodium channels [3]. When all the sodium channels are inactivated, a stimulus is unable to produce an electrical response and this probably accounts for the paralysis observed. The cases reported illustrate the similar occurrence of life-threatening flaccid quadriplegia in hypo- and hyperkalemia. As the potassium concentration in extracellular fluid is a primary determinant of

neuromuscular excitability, serum potassium should be determined in all patients presenting prominent neuromuscular symptoms.

References 1. Gabow PA, Peterson LN (1980) Disorders of potassium metabolism. In: Schrier RW (ed) Renal and electrolyte disorders. Little-Brown, Boston, pp 183-2~1 2. Goldman DE (1943) Potential, impedance and rectification in membranes. J Gen Physiol 27:37 3. Hodgkin AL, Horowicz P (1959) Movements of sodium and potassium in single muscle fibers. J Physiol 146:405 4. Mohamed SD, Chapman RS, Crooks J (1966) Hypokalemia, flaccid quadraparesis and myoglobinuria with carbenoxolone. Br Med J 1:1581 5. Pollen RH, William RH (1960) Hyperkalemic neuromyopathy in Addison's disease. N Engl J Med 263:273 Dr. C. Villabona Gran Via 1101 A 4° 2a E-08020 Barcelona Spain

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