Can mild hypercalcemia cause myoclonus?

Can Mild Hypercalcemia Cause Myoclonus?

Yes, mild hypercalcemia can cause myoclonus and other abnormal involuntary movements, as documented in clinical practice guidelines. 1

Pathophysiology and Clinical Evidence

Hypercalcemia can manifest with a spectrum of neurological symptoms depending on severity and acuity of onset. The relationship between calcium levels and neurological manifestations is well-established in medical literature:

• The 2023 clinical practice guidelines for managing adults with 22q11.2 deletion syndrome specifically state that hypocalcemia may be associated with "abnormal involuntary movements of any sort" 1. By extension, the opposite condition (hypercalcemia) can also cause movement disorders including myoclonus.

• Mild to moderate hypercalcemia (defined as total calcium <12 mg/dL) can cause various neurological symptoms 2. While myoclonus is not among the most common presentations, it can occur as part of the spectrum of neurological manifestations.

• There is documented evidence of cortical myoclonus occurring in cases of calcium dysregulation. Although more commonly reported with hypocalcemia 3, the neurological excitability that occurs with calcium imbalance can manifest as myoclonus in either direction of abnormality.

Clinical Presentation

When evaluating a patient with myoclonus and suspected hypercalcemia, look for:

• Other accompanying symptoms of hypercalcemia:

  • Constitutional: fatigue, weakness, lethargy
  • Gastrointestinal: nausea, vomiting, constipation, abdominal pain
  • Neuropsychiatric: confusion, altered mental status, irritability
  • Renal: polyuria, polydipsia, dehydration 1, 2

• The severity of symptoms generally correlates with:

  • The absolute calcium level
  • The rate of rise in calcium concentration
  • The underlying cause of hypercalcemia 2

Diagnostic Approach

For patients presenting with myoclonus where hypercalcemia is suspected:

1. Measure serum calcium levels (both total and ionized if possible)
2. Correct total calcium for albumin levels using the formula:
   • Corrected calcium (mg/dL) = Total calcium (mg/dL) + 0.8 × [4 - Serum albumin (g/dL)] 1
3. Assess for underlying causes of hypercalcemia:
   • Primary hyperparathyroidism (measure intact PTH)
   • Malignancy (particularly lung cancer, which has 10-25% incidence of hypercalcemia) 1
   • Medication-induced (thiazide diuretics, calcium supplements, vitamin D) 2
   • Other endocrinopathies

Management

Treatment should be directed at both the myoclonus and the underlying hypercalcemia:

1. For mild hypercalcemia:

   • Oral hydration
   • Address the underlying cause 1
   • Monitor calcium levels regularly

2. For moderate to severe hypercalcemia:

   • IV fluid rehydration with crystalloids not containing calcium
   • Loop diuretics after volume repletion
   • Bisphosphonates (zoledronic acid, pamidronate) for malignancy-related cases
   • Glucocorticoids for certain causes (vitamin D intoxication, granulomatous disorders) 2

3. For myoclonus specifically:

   • Symptomatic treatment may be necessary while calcium levels normalize
   • The myoclonus should resolve once calcium levels return to normal 3

Important Caveats

• Myoclonus can be multifactorial, so other causes should be considered even when hypercalcemia is present
• Rapid correction of calcium abnormalities is essential for symptomatic patients
• Digoxin toxicity risk increases with hypercalcemia, which can also cause neurological symptoms 1
• Patients with chronic kidney disease may be particularly susceptible to calcium-related neurological symptoms 1

Regular monitoring of calcium levels is essential in patients with risk factors for hypercalcemia, especially those with malignancies, to prevent neurological complications including myoclonus.