Isolated mitochondrial myopathy is characterized by slowly progressive limb-girdle muscle weakness and resembles other muscle disorders like muscular dystrophy or inflammatory myopathy on clinical grounds. Identification of abnormal mitochondria in the muscle tissue is required for the diagnosis of isolated mitochondrial myopathy. Therefore, this study was done with aim to identify patients with isolated mitochondrial myopathy among those with limb-girdle muscle syndromes of undefined cause. Forty-eight consecutive patients with limb-girdle muscle disease from 2008 to 2010 were screened for Duchenne/Becker muscular dystrophy gene deletion, metabolic myopathy, and drug-induced and endocrine causes. Twenty patients without an identifiable cause were subjected to muscle biopsy for hematoxylin and eosin staining and enzyme histochemistry. Clinical, biochemical, and electrophysiological features in all these patients with limb-girdle muscle disease were nonspecific, and no conclusion regarding the underlying cause could be drawn from these investigations. On hematoxylin and eosin staining, 12 patients were diagnosed as muscular dystrophy, inflammatory myopathy with characteristic appearance of polymyositis was diagnosed in 4 patients, and 3 patients had normal muscle histology. After enzyme histochemistry, one patient was identified having mitochondrial myopathy. A brief case summary of the only patient diagnosed as isolated mitochondrial myopathy in our study is presented.
Mitochondrial syndromes are a group of heterogeneous disorders that affect multiple organ systems. Most mitochondrial syndromes like mitochondrial encephalopathy with lactic acidosis and stroke (MELAS) are clearly defined clinical syndromes which are easily identifiable and can be confirmed by identifying specific genetic mutations in the mitochondrial DNA. However, few newer mitochondrial syndromes like isolated mitochondrial myopathy are increasingly being [
All consecutive patients attending the outpatient department of Neurology at Sanjay Gandhi Postgraduate Institute of Medical Sciences, Lucknow, from November, 2008 to October, 2010 with limb-girdle weakness attributable to muscle disease on the basis of clinical, biochemical, and electrophysiological tests were included in the study. Patients with characteristic clinical features suggestive of muscular dystrophy (e.g., facio-scapulo-humeral muscular dystrophy, congenital muscular dystrophy, congenital myopathy, those with areas of hypertrophy and atrophy in the same muscle, and those with gene mutations positive for Duchenne/Becker muscular dystrophy), inflammatory myopathy (with characteristic skin rash of dermatomyositis, associated immunological disease or malignancy), drug-induced myopathy, osteomalacia associated myopathy, and endocrine myopathy (hypothyroid, hyperthyroid, steroid induced, Cushing’s disease, and acromegaly) were excluded.
Forty-eight patients with limb girdle muscle disease were seen in the above-mentioned period. Twenty-eight patients were excluded (10 patients who tested positive for gene deletion study for Duchenne muscular dystrophy, 12 patients having osteomalacic myopathy, 4 with hypothyroidism-associated myopathy and 2 patients with steroid-induced myopathy). Twenty patients were included in the study.
All 20 patients included in the study were subjected to a muscle biopsy.
Muscle biopsy from either quadriceps (18) or gastrocnemius (2) muscle was obtained under local anaesthesia after obtaining written consent from the patients/relatives. Each muscle biopsy was received fresh in the department of pathology without any additive or fixative. One small piece was fixed in 10% buffered formalin for routine processing and paraffin embedding for hematoxylin and eosin stain. A second piece was immediately snap frozen in precooled isopentane at −80°C. 5-6
Apart from routine hematoxylin and eosin stain, various other histochemical stains were done to identify the muscle disease. These included modified gomori trichrome, oil-red-O, periodic acid Schiff, nicotinamide adenine dinucleotide-tetrazolium reductase (NADH-TR), succinic dehydrogenase (SDH), and cytochrome oxidase (COX).
Patients ranged in age from 8 to 58 years with male to female ratio of 1 : 1. The duration of illness varied from 4 months to 15 years. In addition to progressive shoulder and hip girdle weakness, one patient each had prominent distal weakness, neck flexor weakness, ptosis with external ophthalmoplegia, and bulbar weakness. Other features like retinitis pigmentosa, cardiomyopathy, seizures, and muscle cramps were also seen occasionally (Table
Clinical, biochemical and electrophysiological characteristics of patients with limb-girdle muscle weakness.
Age | Sex | Duration of illness | Pattern of weakness | Family history | Others | CPK (IU/mL) | EMG | |
---|---|---|---|---|---|---|---|---|
(1) | 8 | M | 36 | Proximal | Of IGE (AD) | Ret pig | 75 | Myopathic |
(2) | 14 | M | 96 | Proximal + distal | AR | Iliotibial contractures | 1243 | Myopathic, fibs |
(3) | 33 | M | 120 | Proximal > distal | — | DCMP | 2439 | Myopathic |
(4) | 20 | F | 60 | Proximal + distal | — | Ankle contractures Cramps, GTCS | 528 | Myopathic |
(5) | 12 | F | 60 | Mild proximal | — | Pes cavus | 740 | Normal |
(6) | 34 | F | 180 | Proximal + distal | — | Elbow knee ankle contract. | 179 | Myopathic |
(7) | 16 | M | 108 | Proximal + distal | — | — | 1443 | Myopathic |
(8) | 20 | M | 84 | Proximal > distal | — | Skin changes | 1441 | Myopathic |
(9) | 58 | F | 24 | Proximal + distal + neck flexor | — | — | 600 | Myopathic, fibs, PSW |
(10) | 48 | F | 120 | Proximal | AR | — | 1817 | Myopathic |
(11) | 11 | M | 84 | Proximal > distal | — | Ichthyosis, hyperkeratotic skin, contractures b/l knee, elbow, ankle joints, hepatomegaly | 2500 | Myopathic |
(12) | 35 | M | 36 | Proximal > distal, | AR | HOCM | 110 | Myopathic |
(13) | 15 | F | 60 | Mild proximal + distal | — | Muscle cramps (rest) | 96 | Myopathic |
(14) | 29 | F | 8 | Proximal > distal | — | — | 407 | Myopathic, PSW. Fibs |
(15) | 24 | M | 5 | Proximal > distal | Type 2 DM in father | — | 2500 | Myopathic |
(16) | 26 | F | 8 | Proximal > distal, bulbar | — | Recurrent oral ulcers | 191 | Myopathic RNS −ve |
(17) | 45 | F | 4 | Proximal > distal | — | — | 1628 | Myopathic, PSW, Fibs |
(18) | 37 | F | 12 | Proximal > distal | — | — | 1774 | Normal |
(19) | 8 | F | 7 | Proximal > distal | — | — | 7128 | Myopathic |
(20) | 55 | M | 10 | Proximal > distal | — | Chronic alcoholic and smoker, hypertension 1 year | 109 | Myopathic |
AR—autosomal recessive, AD—autosomal dominant, CPK—creatine phosphokinase, DM—diabetes mellitus, DCMP—dilated cardiomyopathy, F—female, fibs—fibrillations, GTCS—generalized tonic-clonic seizures, IGE—idiopathic generalised epilepsy, M—male, PSW—positive sharp waves, RNS—repetitive nerve stimulation.
Fourteen patients showed maintained fascicular architecture. Fibre size variability was seen in 19 patients, which was more marked in three patients. Necrotic and regenerating fibres were seen in two patients and marked fibrosis was evident in three patients. Interstitial inflammation was seen in seven patients. Fibre type grouping was not identified in any biopsy. Ragged red fibres on modified Gomori Trichrome stain with subsarcolemmal dense staining on NADH/SDH and COX negative fibres were seen in one patient. Criteria used for diagnosis of mitochondrial myopathy were evidence of almost 5% ragged red fibres in 100x magnification field. Histopathological diagnosis was given as muscular dystrophy in 12 patients, inflammatory myopathy in 4 with characteristic appearance of polymyositis in one patient, mitochondrial myopathy in one patient, and normal muscle histology in 3 cases. A brief case summary of the only patient diagnosed as isolated mitochondrial myopathy in our study is presented.
A 35-year-old male complained of progressive symmetrical eyelid drooping, first noticed 20 years ago, and proximal limb weakness for last 5 years. Drooped eyelids covered half of sclera resulting in compensatory neck extension for distant vision. Limb weakness was progressive, producing difficulty in standing from a chair and running. Upper limb weakness was noticed for a year especially on lifting a weight overhead. There was no history of orthopnea, paroxysmal nocturnal dyspnoea, chest pain, pedal oedema, diurnal variation of muscle weakness, diplopia, thinning of limbs, or muscle cramps, impairment in vision, or hearing loss. Patient’s younger sibling, who was 28-year-old, also had a similar drooping of both eyelids for 15 years and dyspnoea on exertion for two years. Dyspnoea was noticed at the beginning of uphill walking or climbing stairs and also after a brisk walk for fifty meters or more. He never noticed any limb weakness. Patient had three female siblings (24, 16, and 12 years old, resp.) who were normal. Patient’s parents and their siblings did not have similar complaints. They had a consanguineous marriage. Patient’s examination revealed incomplete ptosis, external ophthalmoplegia, normal pupil size and light reaction, and normal fundus examination. The rest of the cranial nerves were normal. Mild atrophy of bilateral deltoids, infraspinatus, biceps, first dorsal interossei, quadriceps, and gastrocnemius muscles was noticed. Bilateral winging of scapulae (rhomboids type) was present. Muscle power was grade 3/5 (Medical Research Council scale) in hip and shoulder girdle muscles and grade 4/5 in distal limb muscles. All deep tendon reflexes were reduced, and both plantars were flexors. The rest of the neurological and systemic examination was normal. Examination of patient’s brother revealed similar ocular findings. Similar pattern of muscle atrophy was present, but winging of scapulae was not seen. His muscle power was grade 4/5 in proximal and grade 5/5 in distal limb muscles. Tachycardia and S3 gallop rhythm was noticed on cardiac auscultation. The rest of the systemic examination was normal. Investigations revealed normal haematological and biochemical blood parameters including total CPK and CPK-MB, and pre- and postexercise blood lactate. Nerve conduction tests were normal. Electromyography revealed small polyphasic motor unit action potentials without any spontaneous activity and early complete recruitment on forced voluntary muscle activity. Echocardiography showed presence of hypertrophic and restrictive cardiomyopathy with ejection fraction of 35%. Muscle biopsy findings (Table
Histopathological and enzyme histochemical profile of patients with limb-girdle muscle weakness.
No | H and E | NADH/SDH/COX | MGT | ORO/PAS | Diagnosis | ||||
Architecture | Fiber size variation | Interstitial | Central nuclei | Interstitial inflamm. | Fiber type grouping | Ragged red fibers | Fat/glycogen deposition | ||
1 | Maintained | Present (foal) | Mild | Absent | Absent | Absent | Absent | Absent | Dystrophy |
2 | Maintained | Present | Absent | Absent | Mild | Absent | Absent | Absent | Dystrophy |
3 | Distorted | Marked | Present | Present | Absent | Absent | Absent | Absent | Dystrophy |
4 | Distorted | Moderate | Present | Absent | Absent | Absent | Absent | Absent | Dystrophy |
5 | Maintained | Absent | Occasionl | Absent | Absent | Absent | Absent | Absent | Normal |
6 | Maintained | Present | Mild | Absent | Absent | Absent | Absent | Absent | Dystrophy |
7 | Distorted | Marked | Marked | Absent | Absent | Absent | Absent | Absent | Dystrophy |
8 | Distorted | Marked | Marked | Few | Absent | Absent | Absent | Absent | Dystrophy |
9 | Maintained | Minimal | Minimal | Absent | Minimal | Absent | Absent | Absent | Inflammatory |
10 | Maintained | Present | Minimal | Absent | Absent | Absent | Absent | Absent | Dystrophy |
11 | Maintained | Present | Present | Absent | Absent | Absent | Absent | Absent | Dystrophy |
12 | Maintained | Present | Absent | Present | Absent | Hyperstained NADH, SDH fibers COX negative fibers | >5% | Absent | Mitochondrial myopathy |
13 | Distorted | Present | Present | Present | Present | Absent | Absent | Absent | Dystrophy |
14 | Maintained | Present | Absent | Absent | Present | Absent | Absent | Absent | Inflammatory |
15 | Maintained | Present | Absent | Few | Present | Absent | Absent | Absent | Inflammatory (polymyositis) |
16 | Maintained | Present | Minimal | Absent | Absent | Absent | Absent | Absent | Normal |
17 | Maintained | Mild | Absent | Absent | Present | Absent | Absent | Absent | Inflammatory |
18 | Maintained | Mild | Minimal | Absent | Absent | Absent | Absent | Absent | Dystrophy |
19 | Maintained | Present | Present | Present | Absent | Absent | Absent | Absent | Dystrophy |
20 | Maintained | Mild | Absent | Absent | Mild | Absent | Absent | Absent | Normal |
H and E—hematoxylin and eosin, NADH— nicotinamide adenosine dehydrogenase, SDH—succinic dehydrogenas, COX—cytochrome oxidase, MGT— modified gomori trichrome, ORO—oil red O, PAS— periodic acid Schiff.
Biopsy from quadriceps muscle shows intense staining of fibre with NADH-TR and SDH stain (a, b) and appear white on cytochrome oxidase activity (c). These muscle fibres shows presence of ragged-red fibres with modified Gomori trichrome stain (d).
The first patient with isolated mitochondrial myopathy was recognized by Coleman in the year 1967 [
Clinical, pathological and biochemical characteristics of patients with isolated mitochondrial myopathy with proven mitochondrial mutations.
Age/ Sex | DOI | Limb weakness | Other features | Family history | EMG | Biochemical | Histopathology | Mutation | |
---|---|---|---|---|---|---|---|---|---|
Yang et al. [ | 55/F | — | Mild | Severe respiratory dysfunction | — | Myopathic | — | RRF on MGT | m.A3243G tRNA (Leu(UUR)) |
Hirata et al. [ | 70/M | 20 Y | Proximal | Hypertension, hyperlipidemia | Brother, son | Myopathic | CK 4–10X | RRF on MGT, COX deficient, RC enzymes reduced | A-G transition at np8291 and 9bp del |
64/M | 1Y | Proximal | AMI | Brother of case 1 | Myopathic | CK 4X | Same | Same | |
38/M | 3Y | Proximal | Subcutaneous | Son of case 1 | Myopathic | CK 2-3X | Same | Same | |
71/F | 3Y | Proximal | Hypothyroidism hyperlipidemia | Sister | — | CK 2X | Same | Same | |
52/F | 7Y | Proximal | — | Sister of case 4 | — | CK 10X | Same | Same | |
58/F | 14Y | Proximal | — | — | — | CK 10X | Same | Same | |
42/F | 4Y | Proximal | — | — | — | CK 7X | Same | Same | |
Seneca et al. [ | —/F | — | Exercise intolerance | — | Negative | — | — | RRF, RC enzymes I, IV reduced | m.A7526GtRNA (Asp) |
Swalwell et al. [ | 46/F | 18M | Proximal | Myalgia | Negative | Myopathic | CK 7X, Post ex Lactate 3X | RRF, COX negative fibers | m.5591 G > A tRNA(Ala) |
Meulemans et al. [ | 48/F | — | Proximal | Facial weakness, | Short stature in mother | — | — | RRF on MGT, COX deficient fibers, RC enzymes normal | m.5888 insA & m. 14639 A > G |
Gempel et al. [ | 34/F | 2Y | Proximal | IDDM | Negative | Myopathic | CK 10 X Lactate N | RRF, COX negative, Mus CoQ | ETFDH gene m. |
29/M | 6M | Proximal | Scapular winging | Consanguinity in parents | Myopathic | CK 10X Post ex lactate 10X | Same | Same | |
13/M | — | Proximal | — | Consanguinity in parents | — | CK 20X | Same | Same | |
17/F | — | Proximal | — | — | — | CK 8X | Same | Same | |
12/F | — | Proximal | — | Sister | Normal | CK 40X | Same | Same | |
—/F | — | Proximal | Myalgia | Sister of above case | — | — | Same | Same | |
Leshinsky-Silver et al. [ | 13/F | — | Proximal | — | — | — | CK 5X | Same | Same |
—/— | — | Mild weakness | — | — | — | RRF | H90N m. In TK2 gene |
DOI—duration of illness, F—female, M—male, Y—years, M—months, CK—creatine kinase, X—times normal, RRF—ragged red fibers, COX—cytochrome C oxidase, MGT—modified Gomori Trichrome, m. —mutation.
Bilateral ptosis was seen in the patient described by Meulemans et al. [
On histopathology, we classified our patients into four groups consisting of muscular dystrophy in 12, inflammatory myopathy in four, mitochondrial myopathy in one, and normal histology in three patients. All patients with muscular dystrophy had duration of illness in years except one patient who had a history of seven months. On the contrary, the patients diagnosed as inflammatory myopathy had duration of illness lasting few months. Other findings like limb weakness, creatine kinase levels, electromyography, and other clinical features like skin changes and so forth were not specific to either entity. Those with family history of proximal weakness proved to be muscular dystrophy on histopathology in our study. Three patients who had normal muscle histology possibly either had a muscle biopsy from a nonrepresentative muscle group or had some undetected metabolic myopathy with no characteristic appearance on histopathology.
Muscular dystrophy, inflammatory myopathy, and isolated mitochondrial myopathy have overlapping clinical, biochemical, and electrophysiological features. Enzyme histochemistry should be performed as a routine procedure in addition to Hematoxylin and Eosin stain especially in resource poor countries, where enzyme histochemical staining of muscle biopsy is performed in the selected cases with high clinical suspicion of mitochondrial disorders.