A middle-aged man with a two days history of weakness in his legs. The patient works as a construction worker and is used to conducting heavy physical activity.
After a thorough history and examination, the weakness was reported in the lower extremities with a power of 2/5, whereas the power in upper extremities was 4.5/5, Achilles tendon reflex was reduced, plantar response and other reflexes were intact, with normal sensation. Rest of the examination is unremarkable.
The vitals are within normal ranges, Blood investigations include – Urea and electrolytes, liver and renal function, full blood count, thyroid function tests, creatine kinase, urine myoglobin, vitamin B12 and folic acid levels.
Potassium level was 1.7 mEq/L (normal 3.5-5.5), and all other parameters were within normal ranges.
The ECG showed inverted T waves and the presence of U waves. An Example of an ECG:
Hypokalemic periodic paralysis is a rare disorder that may be hereditary as the primary cause, or secondary due to thyroid disease, strenuous physical activity, a carbohydrate-rich meal and toxins. The patients are mostly of Asian origin.
The most common presentation is of symmetrical weakness in lower limbs, with a low potassium level and ECG changes of hypokalemia. The patients may have a history of similar weaknesses which may be several years old. An attack may be triggered by infections, stress, exercise and other stress-related factors.
The word ‘weakness’, can lead to physicians thinking about stroke, neurological deficits and other life-threatening illnesses such as spinal cord injuries associated with high morbidity and mortality which need to be ruled out in the ED.
In this case, history and examination are vital. Weakness in other parts of the body, a thorough neurological examination are important aspects.
Patients are monitored and treated with potassium supplements (oral/Intravenous) until the levels normalize. ECG monitoring is essential, as cardiac function may be affected.
The patient should be examined to assess the strength and should be referred for further evaluation and to confirm the diagnosis.
The differential diagnosis for weakness in lower limb include :
- Spinal cord disease (https://iem-student.org/spine-injuries/)
- Guillain barre syndrome
- Toxic myositis
- Spinal cord tumour
- Dogan NO, Avcu N, Yaka E, Isikkent A, Durmus U. Weakness in the Emergency Department: Hypokalemic Periodic Paralysis Induced By Strenuous Physical Activity. Turk J Emerg Med. 2016 Mar 2;15(2):93-5. doi: 10.5505/1304.7361.2015.57984. PMID: 27336072; PMCID: PMC4910006.