In the sentence extracted from biomedical literature, identify all the chemical entities. The required answer format is the same sentence with HTML <span> tags to mark up specific entities. 
### Entity Markup Guides:
Use <span class="chemical"> to denote a chemical.

### Input Text: Patients with hypercalcemia resulting from medical diseases and bipolar patients with lithium - associated hypercalcemia had significantly higher frequencies of conduction defects .
### Output Text:
Patients with hypercalcemia resulting from medical diseases and bipolar patients with <span class="chemical">lithium</span> - associated hypercalcemia had significantly higher frequencies of conduction defects . 