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

### Input Text: Our results indicate that DMPK may be necessary for the maintenance of skeletal muscle structure and function and suggest that a decrease in DMPK levels may contribute to DM pathology . .
### Output Text:
Our results indicate that DMPK may be necessary for the maintenance of skeletal muscle structure and function and suggest that a decrease in DMPK levels may contribute to <span class="disease">DM</span> pathology . . 