Mario Bovino1, Jin Young Hwang2, Peter Pytel1, Nitin Nadkarni3, Paul Pritikanta4
1University of Chicago, 2Weiss Memorial Hospital, 3Center Neurological Disease, 4University of Illinois Hospital
Objective:
To describe a rare presentation of amyloid myopathy.
Background:
Wild-type transthyretin amyloidosis (ATTRwt) is an age-related progressive disease with limited treatment options. Cardiomyopathy and peripheral neuropathy are well-recognized manifestations of transthyretin (ATTRwt) amyloidosis but myopathy is rarely the initial presentation.
Results:
An 80-year-old man presented with slowly progressive bilateral lower limb weakness for over 5 years making him bedridden for one year. He denied any oculo-bulbar, sensory, or autonomic symptoms and reported no family history of neuromuscular disease. Physical examination revealed severe symmetric weakness of hip flexors and quadriceps and mild weakness of proximal arms bilaterally. Laboratory workup showed normal CK and no myositis antibodies were detected. Screen for monoclonal protein was negative. EMG performed was consistent with an irritable chronic myopathic process predominantly affecting the proximal leg muscles, along with a mild length-dependent peripheral neuropathy. Right quadriceps biopsy revealed fairly diffuse atrophic changes associated with focal amyloid deposition within adipose tissue and the blood vessel wall without any inflammation. Mass spectrometry suggested ATTR type amyloid and TTR genetic testing was negative confirming diagnosis of ATTRwt amyloid myopathy. A cardiac PYP scan showed diffusely increased myocardial uptake of the radiotracer. Patient was started on Tafamidis by cardiologist to slow disease progression.
Conclusions:
Neurological manifestations of ATTRwt are being increasingly recognized but myopathy is rarely reported as an initial presentation. The clinical presentation of myopathy can mimic other relatively common neuromuscular disorders and hence a high index of suspicion and through workup is needed to confirm diagnosis. Patients can have concomitant cardiomyopathy, which is potentially treatable, and therefore increased awareness is required. Supportive therapy remains the mainstay of therapy for neurological involvement, but future studies can pave the way for targeted treatments.