From the Guidelines

Prednisone and acyclovir is the recommended treatment for a patient with Bell's palsy and uncontrolled diabetes.

The use of oral steroids, such as prednisone, is strongly recommended for patients 16 years and older with new-onset Bell’s palsy, as it has been shown to decrease recovery time and improve facial nerve functional recovery 1.
Acyclovir may be offered in addition to oral steroids within 72 hours of symptom onset, as some studies suggest a possible benefit of combination therapy, although the evidence is not as strong as for steroids alone 1.
Antiviral monotherapy is not recommended, as high-quality randomized controlled trials have shown no benefit over harm 1.

Prednisone can be prescribed at a dose of 25 mg twice daily for 10 days or 60 mg per day for 5 days, then tapered over 5 days 1.
Acyclovir can be prescribed in addition to prednisone, although the optimal dose and duration are not specified in the guidelines.

While the guidelines do not specifically address the treatment of Bell's palsy in patients with uncontrolled diabetes, the use of prednisone and acyclovir is still recommended, as the benefits of treatment are likely to outweigh the risks.
However, patients with uncontrolled diabetes should be closely monitored for any changes in their blood sugar levels and adjusted accordingly.

From the Research

The use of prednisone and acyclovir in treating Bell's palsy has been studied in several research papers 2, 3, 4, 5, 6.
According to a study published in the New England Journal of Medicine, early treatment with prednisolone significantly improves the chances of complete recovery at 3 and 9 months, while acyclovir given alone or in combination with prednisolone does not provide any additional benefit 3.
Another study published in Nature Clinical Practice Neurology also suggests that prednisolone improves outcome in patients with Bell's palsy, but antiviral drugs such as acyclovir do not have a significant beneficial effect 4.
A randomized controlled trial published in the Health Technology Assessment journal found that oral prednisolone is an effective treatment for Bell's palsy, while treatment with aciclovir, either alone or with steroids, had no effect on outcome 5.
However, a study published in the Iranian Journal of Child Neurology found that combined prednisolone and acyclovir therapy is more effective than treatment with prednisolone alone in children with Bell's palsy 6.

A study published in the Canadian Journal of Diabetes found that diabetes does not affect the severity, recovery rate, or healing of Bell's palsy, and all patients with Bell's palsy were prescribed prednisone and acyclovir regardless of their diabetes status 2.
There is no direct evidence to suggest that patients with uncontrolled diabetes should be treated differently than those without diabetes, but it is essential to consider the potential impact of prednisone on blood sugar levels.

Based on the available evidence, prednisone is the recommended treatment for Bell's palsy, and its use should be considered in patients with uncontrolled diabetes, taking into account the potential effects on blood sugar levels 3, 4, 5.
The use of acyclovir in combination with prednisone may not provide any additional benefit, but it may be considered in certain cases, such as in patients with a high risk of viral infection 3, 5.