Theologian RT Kendall is asking supporters for prayers as his wife battles severe back pain.

The Christian writer and speaker revealed on Twitter that his wife Louise is suffering from sciatica, which affects a nerve running from the lower back down the back of the legs.

Kendall, the former pastor of Westminster Chapel, said Louise was 'suffering the worst pain we can recall in 60 years of marriage'.

He has made several appeals for prayers ahead of a scheduled MRI scan at Vanderbilt Clinic on Wednesday.

In the past few days, he posted several tweets about applying the Bible's teaching to stay joyful in trials.

'I have preached for 40 years that we must dignify the trial; we are having to practice this now. Louise is in great sciatica pain. Please pray for her,' he said on Sunday.

Then in the following days, he again referred to James in light of his wife's condition.

'James said that we should count it all joy when we face trials. "Count" means to "impute", same word used regarding righteousness being imputed to us,' he said.

He added: 'It is one thing to "preach" counting it all joy to a trial, another to apply it! We are having to do just that these days! But do pray for us.'

According to Mayo Clinic, sciatic pain most commonly occurs when the nerve is compressed by a herniated disk, bone spur on the spine, or narrowing of the spine.

Although mild sciatica can often go away by itself, more severe cases can require surgery.