Muscular dystrophy and fibromyalgia

Dystrophin is a long, rod-shaped protein that sits just inside the sarcolemma, the membrane of a muscle fibre, and links the internal cytoskeleton to a complex of glycoproteins that reaches out to the surrounding connective tissue. That linkage is what keeps the membrane from tearing when the fibre contracts. Without dystrophin, the mechanical stress of every contraction opens microscopic breaches in the sarcolemma, calcium floods into the fibre, and calcium-activated proteases begin to digest the cell from within. The fibre swells, leaks its contents — which is why creatine kinase appears in the blood — and eventually dies. Muscle has a repair mechanism, but it depends on satellite cells, and in the dystrophinopathies those cells divide repeatedly until they can no longer keep pace.

What replaces the dead fibres is not new muscle but adipose and fibrous tissue, laid down by fibroblasts and inflammatory macrophages. That replacement explains the physical sign that puzzles beginners most: pseudohypertrophy. The calf, and especially the gastrocnemius, looks larger than normal because it is packed with fat and scar, not because it is strong; the same process thickens the tongue and the muscles of the shoulder girdle. The clinical course follows from that biology. In the most common severe form, boys are usually unable to walk by their early teens, and the disease later takes the respiratory muscles and the heart, causing a cardiomyopathy and rhythm disturbances; a milder allelic form, produced by a mutation that keeps the reading frame of the gene intact, allows partial dystrophin and a much slower course.

Two quantitative facts keep the picture concrete: the severe form affects roughly one boy in every 3,500 to 5,000 male births, and corticosteroid treatment buys months to years of walking rather than preventing the outcome. Because the same protein story also threatens the heart and the ventilatory muscles, echocardiography, electrocardiography and lung function become routine surveillance, and the nursing plan must include bone protection, since the corticosteroids that slow the weakness also cause vertebral fractures and weight gain.

Pain is not a direct reading of tissue damage; it is a signal built by the nervous system. Nociceptors, the free nerve endings that detect potentially harmful stimuli, send impulses to the dorsal horn of the spinal cord, where the signal can be turned up or down before it travels by ascending pathways to the brain. The brain also sends descending pathways that normally damp the incoming signal. In fibromyalgia this balance is shifted. Repeated or intense input, physical or emotional stress, and disturbed sleep leave the dorsal horn more excitable, a state called central sensitisation: the same stimulus now produces a larger response. Glutamate acting at NMDA receptors and the neuropeptide substance P amplify transmission in the cord, while the descending, serotonin- and noradrenaline-dependent inhibition that should quieten it is weaker.

The result is hyperalgesia, in which a mildly painful stimulus hurts far more than it should, and allodynia, in which a stimulus that is not normally painful at all — a light touch or the pressure of clothing — is felt as pain. Sleep studies show the disturbance objectively: patients spend less time in deep slow-wave sleep, electroencephalography shows intrusions of alpha rhythm, and the loss of restorative sleep itself increases pain sensitivity the next day. Stress hormones follow the same loop, with a flattened cortisol rhythm along the hypothalamic–pituitary–adrenal axis. This mechanism explains the answers patients find hardest to accept.

There is no inflammation, no erosion and no destructive process, so the erythrocyte sedimentation rate, C-reactive protein, X-rays and muscle enzymes are all normal, and a normal result does not mean the pain is invented. It also explains why fibromyalgia is diagnosed clinically, from the number of painful regions and the severity of fatigue and cognitive symptoms rather than from a laboratory value, and why the same patient often reports irritable bowel, migraine, temporomandibular pain and chronic fatigue. Because several diseases can imitate it — hypothyroidism, rheumatoid arthritis and other connective tissue diseases, myositis and, rarely, malignancy — the first task is always to exclude them, and only then to treat the sensitised system.

The nursing priorities diverge, and each set follows directly from the biology. In muscular dystrophy the muscles that fail last are the ones that kill first, so respiratory surveillance is the core of safe care: measure lung volumes and peak cough flow, watch for a weak cough, retained secretions, morning headache and sleepiness, teach airway clearance, and know when non-invasive ventilation is needed. The heart is monitored with echocardiography and electrocardiography because cardiomyopathy and arrhythmia can progress silently. Muscles that are no longer used shorten into contractures, so the nurse maintains range of motion, uses orthoses and correct positioning, and prevents the pressure injuries and falls that follow weakness and immobility.

Corticosteroid therapy adds its own checklist: weight, blood pressure, blood glucose, bone protection with vitamin D and bisphosphonates, and cataract screening. Family care includes genetic counselling and a pedigree that identifies other carriers, because an apparently healthy relative may be at risk of having an affected son. In fibromyalgia the nursing task is almost the reverse: the examination is normal, so the nurse must validate a pain that has no visible sign, and the risk is that the patient is disbelieved and disengages from care. Assess pain, function, sleep and mood with the same seriousness given to any other symptom, agree a paced programme of graded exercise and aquatic therapy rather than rest, and support cognitive behavioural approaches that reduce distress and improve sleep.

Opioid analgesics are not recommended because they worsen pain over time and carry dependence, tolerance and withdrawal risks, and they are a common and avoidable harm in this group. The medicines that do help — the serotonin–noradrenaline reuptake inhibitors duloxetine and milnacipran, the tricyclic amitriptyline, the muscle relaxant cyclobenzaprine and the anticonvulsants pregabalin and gabapentin — each carry side effects the nurse must teach: nausea, dry mouth, drowsiness, dizziness and weight change. Finally, keep the red flags in view: weight loss, fever, joint swelling, morning stiffness lasting more than an hour, focal neurological signs or a raised inflammatory marker mean the diagnosis is not fibromyalgia and the search must continue.