Neurology India Medknow Publications on behalf of the Neurological Society of India ISSN: 0028-3886 EISSN: 1998-4022 Vol. 58, Num. 2, 2010, pp. 325-326

Neurology India, Vol. 58, No. 2, March-April, 2010, pp. 325-326

Letter To Editor

A case of amyloid myopathy masquerading as inflammatory myopathy

Abhijit Das¹, Anita Mahadevan², Asha Kishore¹, SK Shankar²

¹ Department of Neurology, Sree Chitra Tirunal Institute of Medical Sciences and Technology, Trivandrum, India
² Department of Neuropathology, National Institute of Mental Health and Neurosciences, Bangalore, India

Correspondence Address: Abhijit Das, Department of Neurology, Sree Chitra Tirunal Institute of Medical Sciences and Technology, Trivandrum, India, abhijit.neuro@gmail.com

Date of Acceptance: 15-Sep-2009

Code Number: ni10085

PMID: 20508365

DOI: 10.4103/0028-3886.63781

Sir

Amyloid myopathy is increasingly being recognized as a cause of proximal and, rarely, distal myopathy. ^[1],[2],[3] The clinicians and pathologists need to be more aware of this entity as it can be missed with routine light microscopy. We report a case of amyloid myopathy that was initially misdiagnosed as a case of inflammatory myopathy. This case highlights the need of awareness about amyloid myopathy, especially its distinct clinical features.

A 39-year-old male came to the neuromuscular clinic with a diagnosis of inflammatory myopathy, for a second opinion. He complained of progressive difficulty in getting up from the squatting posture and difficulty in lifting heavy objects for the last six months. He also had difficulty in opening the mouth for the same duration. He noted difficulty in speaking, protruding the tongue out and moving the tongue inside the mouth. He lost 6 kg of weight over this period. There were no other neurological or systemic symptoms and the family history did not reveal any neurological illness. He was taking thyroxine for primary hypothyroidism and was in euthyroid status. The muscle biopsy was performed elsewhere and was interpreted as suggestive of inflammatory myopathy. However, the oral symptoms were not given importance previously by the patient or the referring physician.

On examination, he had restricted oral opening and limited protrusion of the tongue with macroglossia. There was no muscle atrophy or hypertrophy. He had mild proximal weakness in the limb-girdle distribution, grade 4/5 in shoulder and hip muscles. Other clinical examination was normal. Routine investigations, including hemogram, liver and renal function tests, serum creatinine kinase and serum protein electrophoresis were normal and immunoscreening for connective tissue disorders was negative. Electromyography was suggestive of primary myopathic disease. Contrast computed tomography (CT) of the neck and chest was normal. A screening for abdominal or pelvic mass by ultrasound was negative.

In view of the macroglossia, a clinical suspicion of amyloidosis was considered and the muscle biopsy was reviewed. The biopsy from quadriceps showed well-preserved fascicles on histopathological examination. A single focus of moderately dense collection of lymphomononuclear cells was seen surrounding a myofiber that showed signs of regeneration [Figure - 1]a. Most likely, based on these findings, the initial diagnosis of inflammatory myopathy was offered previously. However, the special stains (Congo red) for amyloid were carried out this time, which showed congophillic amyloid deposits in the endomyseal vessels [Figure - 1]b as well as in the epimyseal vessels and collagen [Figure - 1]c. Intriguingly, even the inflamed regenerating myofiber showed presence of amyloid deposits along the sarcolemma [Figure - 1]d. All deposits were strongly birefringent on polarized microscopy. However, the patient was lost to follow-up and further investigations could not be performed.

This case highlights the need of awareness about amyloid myopathy among the neurologists, especially its clinical features. Amyloid myopathy is increasingly being recognized as a cause of proximal myopathy. It can manifest as two phenotypes: the common form, presenting with macroglossia and muscle pseudohypertrophy or a palpable mass within the muscle and a less common form manifesting as progressive muscle weakness without concomitant pseudohypertrophy or macroglossia. ^[1] Our patient had overlap of these two features, but without pseudohypertrophy. Distal muscular atrophy had also been described. ^[2] Weight loss is a common complaint. Signs or symptoms of systemic amyloidosis may or may not be present when the muscle symptoms appear. The occurrence of extra-musculoskeletal symptoms correlating with the duration of the weakness also may or may not be seen. In some patients, slowly progressive weakness may be the only symptom for years while others may have symptoms consistent with amyloidosis soon after the onset of weakness. ^[3] Most of the patients reported had primary or AL amyloidosis and about half harbored a plasma cell dyscrasia or multiple myeloma, identified as the source of immunoglobulin light chain. ^[3]

The clinicians and pathologists need to be more aware of this entity as it can be missed with routine light microscopy. Small amounts of mononuclear inflammatory cells in endomysium or perivascular spaces without invasion of nonnecrotic muscle fibers may be seen, leading to an erroneous diagnosis of polymyositis. ^[1],[3] As further treatment and prognosis is radically different, the recognition of amyloid deposition is the key.

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