Sir, Lithium is a commonly prescribed mood stabilizer in psychiatry. Most side effects of lithium are due to competitive action with potassium.1 Hypokalemic periodic paralysis (HPP) is a rarely reported side effect of lithium that can be fatal if not detected and treated early. Although serious side effects are expected at toxic levels of lithium, HPP can occur at normal serum levels. Here, we describe a lithium-induced HPP in a patient with bipolar affective disorder (BPAD), which, to our knowledge, is the third reported case. A 41-year-old male with no comorbidities, diagnosed with BPAD for 10 years and in remission, presented to the casualty with sudden-onset weakness in upper and lower limbs, more proximal than distal, progressing to difficulty in neck holding within 1 day. He was not on any medication for the past 3 months other than lithium 700 mg as a mood stabilizer. There was no history of fever, headache, slurred speech, facial deviation, bowel or bladder symptoms, trauma, or history of weakness in the family. General examination, including vitals, was normal. Systemic examination revealed reduced tone, 2/5 power, and 1+ reflexes in all four limbs, with a normal sensory system. The mental state examination was unremarkable, with no signs of lithium toxicity. Investigations revealed hypokalemia (2.30 mmol/l) with normal levels of lithium (0.5 mEq/l), sodium, magnesium, and calcium on the day of admission. The ECG revealed ST depression with U wave due to hypokalemia. Creatine phosphokinase (538 U/L), ESR (5 mm/hr), serum creatinine (0.8 mg/dL), and thyroid function tests were normal. Arterial blood gas revealed metabolic acidosis with a urine anion gap of 22, indicating distal renal tubular acidosis (RTA). Naranjo adverse drug reaction probability scale indicated the role of lithium (score: 7) as “probable.” After medicine and nephrology referrals for hypokalemia and RTA, the patient was diagnosed with HPP secondary to lithium-induced distal RTA. Potassium levels were corrected, and lithium tablets were discontinued, which alleviated paralysis. The patient was started on sodium valproate tablets as a mood stabilizer and is doing well during subsequent follow-ups. HPP is a rare disorder, with a prevalence of 1 in 100,000, usually affecting the lower limbs more than the upper limbs, sparing bulbar and ocular muscles. Although respiratory muscles are usually spared in HPP, their involvement can pose life-threatening risks, especially in severe cases.1 Lithium can disrupt acid–base regulation, resulting in renal impairment.2 While nephrocalcinosis and autoimmune disease are the predominant causes of distal RTA, lithium can also cause distal RTA, leading to hypokalemia and periodic paralysis. Despite the known association of lithium with hypokalemia and distal RTA, this is the third reported case of lithium-induced HPP to our knowledge, showing the paucity of research.3–5 The rapid onset and severity of paralysis in our patient, who had no prior history of HPP and was in remission, highlight the necessity for awareness regarding rare but serious risks associated with lithium, like HPP. Therefore, lithium must be suspected as a possible cause when encountering similar atypical presentations in clinical practice. Declaration of patient consent The authors certify that they have obtained all appropriate patient consent forms. In the form, the patient(s) has/have given his/her/their consent for his/her/their images and other clinical information to be reported in the journal. The patients understand that their names and initials will not be published and due efforts will be made to conceal their identity, but anonymity cannot be guaranteed. Financial support and sponsorship Nil. Conflicts of interest There are no conflicts of interest.
Balagopal et al. (Sun,) studied this question.