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We report here an uncommon case of amyloid myopathy presenting with atrophic proximal muscle weakness. The patient had an IgGκ monoclonal gammopathy and plasmacytosis in the bone marrow. Some of the clinical features of the disorder are highlighted in the present case.
A 57 year old man presented with decreased appetite for seven months, difficulty in getting up from a sitting position for three months, and oedema of his feet for two days. He had particular difficulty in getting up in an Indian toilet. He was not a known diabetic or hypertensive and did not smoke or drink alcohol. On examination, there was wasting of shoulder girdle muscles—deltoid, supraspinatus, infraspinatus, pectorals, rhomboids, and biceps with grade III (MRC) power (fig 1). There was also wasting and weakness of pelvic girdle muscles and glutei with grade IV (MRC) power. Deep reflexes were present and sensations were intact. Plantar flexor reflexes were normal.
There were no fasciculations and no pseudohypertrophy of muscles, nodular lesions, or macroglossia. Higher centres and cranial nerves were intact. There was also bilateral pedal oedema, no ascites, a normal jugular venous pulse pressure, and no lymphadenopathy or hepatosplenomegaly.
Clinical investigations were as follows: haemoglobin 10 g/dl, total leucocyte count 7900/ mm3, differential leucocyte count polymorphonuclear cells 68%, lympocytes 30%, eosinophils 2% monocytes 0%, urinary proteins 18 g/l, total proteinuria in 24 hours 7.2 g, Bence Jones proteins absent, total serum proteins 52 g/l, albumin 19 g/l, calcium 8.5 mg/dl (repeat concentration after one week 6.8 mg/dl). Blood urea nitrogen and serum creatinine, sodium, potassium, and phosphorus concentrations were normal. Serum creatine phosphokinase was 142 IU/l (normal value <109 IU/l at 30°C).
Chest radiography showed mild cardiomegaly. No osteolytic lesions were present on skull radiography. Echocardiography showed gross concentric hypertrophy of the ventricles with a bright speckled appearance of the myocardium, trivial tricuspid regurgitation, small pericardial effusion, and ejection fraction 40%. ECG disclosed low voltage complexes with sinus rhythm. Ultrasound of the abdomen showed loss of corticomedullary differentiation in the kidneys with free fluid in the abdominal cavity. EMG disclosed polyphasic muscle action potentials, decreased interference pattern, and no spontaneous activity, consistent with myopathy. Serum electrophoresis showed an M band in the γ region. Immunofixation showed the monoclonal gammopathy to be of the IgG κ type. The concentration of M protein was 36.14 g/l, IgM 0.16 g/l , and IgA 0.13 g/l . Bone marrow aspiration showed an increased number of plasma cells (19%). Muscle biopsy from the quadriceps femoris showed considerable deposition of amorphous material between muscle fibrils with compression of the fibrils and loss of fibril details, which showed characteristic staining of amyloid with Congo red and crystal violet stains (fig 2).
On the sixth day in hospital, the patient developed breathlessness with orthopnoea and cough. Oedema in his feet increased. He was started on frusemide and lisinopril. However, he continued to have episodes of breathlessness on lying down. His weakness also gradually increased and he encountered increasing difficulty in standing up. The dose of diuretic drugs was increased. The patient felt better. Predisone (40 mg/day) and cyclophosphamide (150 mg/day) were added and he was discharged on the 21st day in hospital. About a month after discharge the patient developed severe breathlessness and collapsed and died at home. A postmortem could not be carried out
The differential diagnosis of proximal muscle weakness at this age would include polymyositis, inclusion body myositis, and anterior horn cell disease (progressive muscular atrophy). The clinical findings, paraproteinaemia, and the characteristic histological findings, however, make these diagnosis untenable in this patient.
Amyloid myopathy has come to be recognised in recent years as a distinct cause of proximal muscle weakness. It usually occurs in cases with primary amyloidosis (AL type). The disorder is not common. In a retrospective analysis of cases over a 27 year period at the Mayo Clinic, only 12 cases of amyloid deposit in the muscle were seen.1
This case highlights some of the clinical features of amyloid myopathy. It is important to appreciate that the disorder often presents with atrophic proximal muscle weakness, as seen here and reported by others.1-4 Pseudohyopertrophy, nodular lesions of muscles, and macroglossia are often not seen. Also it may be worth noting that the predominant manifestation initially may be only of proximal muscle weakness and other manifestations due to amyloid deposition at other sites may develop only subsequently.
The long term prognosis in such cases is poor as seen in this case and reported by others.. Median survival is 4.9–14.7 months from diagnosis.5 Response to cytotoxic agents is also poor. Death usually occurs due to cardiac arrhythmias or progressive cardiac failure. The disorder needs to be considered in all elderly persons presenting with atrophic proximal muscle weakness.