Differential Diagnosis of Weakness

(Image credit: McGhee, Evidence Based Physical Diagnosis, 3rd Edition.)

Today, we discussed a very interesting case of gradual onset of diffuse weakness accompanied by a diffuse rash on a background of cancer. This case seemingly was of dermatomyositis, though the diagnosis was unclear. In general, the differential diagnosis for weakness can be summarized succinctly in a 4x4 table, whereby each diagnosis is stratified by lesion location and pathologic category: