Hypokalaemic periodic paralysis secondary to subclinical hyperthyroidism: an uncommon cause of acute muscle paralysis

Hypokalaemic periodic paralysis secondary to subclinical hyperthyroidism is an uncommon clinical phenomenon characterised by lower limb paralysis secondary to hypokalaemia in the background of subclinical hyperthyroidism. In this article, we report a patient who presented with progressive lower limb muscle weakness secondary to hypokalaemia that was refractory to potassium replacement therapy. He has no diarrhoea, no reduced appetite and was not taking any medication that can cause potassium wasting. Although he was clinically euthyroid, his thyroid function test revealed subclinical hyperthyroidism. His 24-hour urine potassium level was normal, which makes a rapid transcellular shift of potassium secondary to subclinical hyperthyroidism as the possible cause. He was successfully treated with potassium supplements, non-selective beta-blockers and anti-thyroid medication. This case report aimed to share an uncommon case of hypokalaemic periodic paralysis secondary to subclinical hyperthyroidism, which to our knowledge, only a few has been reported in the literature.

A 29-year-old Bodybuilder with Liothyronine-induced Thyrotoxic Hypokalaemic Periodic Paralysis

We describe a 29-year-old male bodybuilder with recurrent attacks of myalgia and muscle weakness associated with hypokalaemia and thyrotoxicosis due to abuse of liothyronine. The attacks quickly resolved after potassium supplementation and liothyronine cessation. We concluded that the patient had thyrotoxic hypokalaemic periodic paralysis (TPP). Although muscle weakness and hypokalaemia are prominent symptoms of TPP, underlying thyrotoxicosis may be overlooked. Up to 25% of androgen abusers also abuse thyroid hormone. Lack of recognition of thyroid hormone abuse as a cause of hypokalaemic periodic paralysis may result in unnecessary, potentially harmful medical investigations and improper treatment and advice.

Hypokalaemic periodic paralysis with a charge-retaining substitution in the voltage sensor

Familial hypokalaemic periodic paralysis is a rare skeletal muscle disease caused by the dysregulation of sarcolemmal excitability. Hypokalaemic periodic paralysis is characterized by repeated episodes of paralytic attacks with hypokalaemia, and several variants in CACNA1S coding for CaV1.1 and SCN4A coding for NaV1.4 have been established as causative mutations. Most of the mutations are substitutions to a non-charged residue, from the positively charged arginine (R) in transmembrane segment 4 (S4) of a voltage sensor in either CaV1.1 or NaV1.4. Mutant channels have aberrant leak currents called ‘gating pore currents’, and the widely accepted consensus is that this current is the essential pathological mechanism that produces susceptibility to anomalous depolarization and failure of muscle excitability during a paralytic attack. Here, we have identified five hypokalaemic periodic paralysis cases from two different ethnic backgrounds, Japanese and French, with charge-preserving substitutions in S4 from arginine, R, to lysine, K. An R to K substitution has not previously been reported for any other hypokalaemic periodic paralysis families. One case is R219K in NaV1.4, which is located at the first charge in S4 of Domain I. The other four cases all have R897K in CaV1.1, which is located at the first charge in S4 of Domain III. Gating pore currents were not detected in expression studies of CaV1.1-R897K. NaV1.4-R219K mutant channels revealed a distinct, but small, gating pore current. Simulation studies indicated that the small-amplitude gating pore current conducted by NaV1.4-R219K is not likely to be sufficient to be a risk factor for depolarization-induced paralytic attacks. Our rare cases with typical hypokalaemic periodic paralysis phenotypes do not fit the canonical view that the essential defect in hypokalaemic periodic paralysis mutant channels is the gating pore current and raise the possibility that hypokalaemic periodic paralysis pathogenesis might be heterogeneous and diverse.

Parésia Hipocaliemica em Adolescente: Um Caso Clínico

Familial hypokalaemic periodic paralysis is a rare autosomal dominant neuromuscular disease characterized by episodic attacks of flaccid paralysis with concomitant hypokalaemia. We present a case of a 15-year-old male adolescent observed in the pediatric emergency department by flaccid paresis of the 4 limbs of sudden onset and progressive worsening. In the anamnesis, corticosteroid and antihistamine intake were observed on the previous day for urticaria and family history of transient episodes of flaccid paralysis in adolescence, asymptomatic after the fourth decade of life, without an established diagnosis. Diagnostic tests revealed hypokalaemia (K + < 2.4 mEq/L), without hypokaluria and without other changes. Symptomatology resolution after supplementation with potassium was verified until normalization of kaliemia. Flaccid paralysis is a rare form of presentation of hypokalaemia. Several etiologies may be involved in the child or adolescent presenting with acute flaccid paralysis. The description of this case draws attention to the importance of the knowledge of this entity, because if recognized and treated properly, patients usually recover without sequelae.