What are the potential pitfalls of using outdated PHP syntax in class inheritance?

Using outdated PHP syntax in class inheritance can lead to compatibility issues with newer versions of PHP, as well as potential security vulnerabilities. To solve this issue, it is recommended to update the code to use the latest PHP syntax for class inheritance, such as using the `extends` keyword.

// Outdated PHP syntax for class inheritance
class ParentClass {
    // Class implementation
}

class ChildClass extends ParentClass {
    // Class implementation
}
``` 

```php
// Updated PHP syntax for class inheritance
class ParentClass {
    // Class implementation
}

class ChildClass extends ParentClass {
    // Class implementation
}