Systemic light chain amyloidosis myopathy responsive to daratumumab monotherapy

Background and purpose: Amyloid myopathy is a rare and severe manifestation of systemic light chain ( AL) amyloidosis. Early diagnosis and staging are mandatory for optimal therapy, given the rapid progression of muscle weakness. Despite the efficacy of bortezomib--based treatment regimens, there is a lack of therapeutic alternatives in non-responsive patients. Method: The case report of a patient with systemic AL amyloidosis myopathy treated with daratumumab is presented. Results: A 70--year- -old man displayed severe proximal muscle weakness which had developed over a 10--month period. Blood tests revealed an immunoglobulin A lambda monoclonal gammopathy, whilst muscle biopsy showed amyloid deposits within the arteriolar walls, confirming the diagnosis of amyloid myopathy associated with AL amyloidosis. Initial treatment with a bortezomib--based regimen showed no clinical or hematological improvement. After switching to daratumumab monotherapy, our patient achieved a favorable evolution with respect to functional muscle scoring and a complete hematological response. Conclusion: To our knowledge, this is the first case report of an amyloid myopathy showing a remarkable clinical improvement in response to daratumumab monotherapy. It thereby highlights the potential of daratumumab as a monotherapeutical approach to the treatment of amyloid myopathy complicating AL amyloidosis.