"difficulty has grown" is correct and usable in written English.
You can use it when you need to describe a situation in which something became more difficult. An example sentence might be: "As the competition in the market has increased, the difficulty of succeeding as an independent business owner has grown."
In the latest of short updates on Chavez's health, the government said last week his breathing difficulties had grown worse, and he was using a tracheal tube.
Despite these difficulties, Buurtzorg has grown extremely rapidly, after ten years following its inception there are over 10 000 nurses working for Buurtzorg, and it has been voted to be the best employer in Holland every year since 2011 (Table 2).
Lesson # 3: No matter what our current difficulties may be, someone else has grown from a difficulty like it -- and so can we.
And hence, Whole Foods' difficulty in conceding that as it has grown up -- and with it, the entire organic food industry -- it has had to accept some compromises along the way.
But as demand has grown, so has the difficulty of finding and vetting qualified people.
If we bear in mind that Aristotle approaches all these activities within the broader context of his teleological explanatory framework, then at least some of the highly polemicized interpretative difficulties which have grown up around his works in this area, particularly the Poetics, may be sharply delimited.
Of course the clarion call of American greatness can be a distraction from economic difficulty, but Americans have grown wary of adventure.
The critics descending on Washington argue that the I.M.F. and the World Bank sometimes made these crises worse, while their defenders assert that without the difficulties inflicted, the crises would have grown worse.
But the pain did not subside it had grown worse: Guy walked with difficulty.
Key Womenswear sales have grown, while a recent improvement in online sales, despite previously flagged difficulties, provides some relief.
I finally realised that the difficulties I'd had growing up were much less to do with me than to do with her being a deeply troubled, paranoid woman.
