Tumors reported to cause the condition:
(1) non-small cell lung carcinoma
(2) breast cancer
(3) prostate adenocarcinoma
(4) adenocarcinoma of the gastrointestinal tract
(5) urothelial carcinoma
Clinical features:
(1) The patient develops a proximal, symmetrical weakness that is rapidly progressive.
(2) The onset of muscle symptoms may precede or follow the diagnosis of cancer.
(3) Examination of the affected muscles shows weakness and atrophy.
(4) The deep tendon reflexes are hypoactive.
(5) The patient develops disability related to the affected muscles.
EMG findings are consistent with a myopathy with poor activation during voluntary contraction.
Histologic changes in a muscle biopsy:
(1) extensive necrosis of involved muscles
(2) absence of a vasculitis or inflammatory cell infiltrate
Laboratory testing shows elevation in serum levels of muscle markers (myoglobin, creatinine kinase, etc).
Differential diagnosis:
(1) other paraneoplastic conditions such as dermatomyositis
(2) tumor infiltration of nerves
(3) viral myopathy
