The pathological phenotypes may be masked or less prominent following long-term corticosteroid treatment, of over around 2 weeks duration. However, if the patient has received steroids, it is advisable to still go ahead with the biopsy but remember to indicate in the request form that the patient was treated with steroids, so this can be taken into account during interpretation.  Prolonged corticosteroid use may lead to steroid-induced myopathy