Frequent Falls - Muscle disease
Freddie is a 4 year old boy who seems to fall over a lot in the play ground and doesn’t run as fast as his friends. Mum has noticed that Freddie’s stamina is reduced as he often asks to be carried when they are out shopping. Freddie never complains of any pain in his legs. He has not lost any weight recently and generally is very well.
Freddie was born full term. He is the first child in the family. Both mum and dad are well and they are not aware of any significant illnesses in the family.
Freddie was well at birth and mum described him as a thriving and chubby baby who breast fed well. He rolled at 6 months and pulled up to stand at 14 months. He cruised at 16 months and walked at 20 months. He started talking in short sentences at the age of 3 and is currently awaiting a speech and language assessment as pre-school.
Mum talks to the health visitor about Freddie and she advises that he is checked by the GP.
The GP observes Freddie walking into the consultation room and notices a broad based gait. Freddie is walking well but seems unsteady on his legs when picking up a toy from the floor. He seems to push himself up on his legs to get himself up. His height and weight are both on the 50th centile.
On inspection, Freddie has large calf muscles. There is no muscle wasting. His skin looks unremarkable with no bruising and no rash.
Examination of his musculoskeletal system seems unremarkable (pGALS). His joint examination is normal; there is no swelling, redness or increased temperature in any of his joints. He has a normal range of movements in both his arms and legs. There is no stiffness in any of the joints.
Further examination does not reveal any abnormalities. His respiratory, cardiovascular and abdominal examination are unremarkable. The GP attempts a neurological examination and does not detect any obvious abnormalities in reflexes, tone and power.
- Slightly delayed motor development
- Frequent falls
- Seems to struggle to get up from the floor, using hands to “walk up legs” (Gower sign)
- Mild speech delay
- Broad based gait in a child > age 2. This is abnormal and may indicate muscle weakness
- Delayed walking by 18 months raises concerns
- Enlarged calves (calf hypertrophy); this is typically seen in Duchenne muscular dystrophy and is due to fat and connective tissue that have replaced damaged muscle cells
- The child may be 'floppy' with reduced muscle tone (hypotonia) but this can be difficult to detect in young children
- The combination of waddling gait, frequent falls, mildly delayed motor development and mild speech delay point to a muscle disorder (myopathy). There are many different types but the most common is Duchenne muscular dystrophy.
- Creatine kinase; this test is a highly useful test for muscular dystrophies (often elevated 10-100x), and it is elevated from birth. If CK is normal then muscular dystrophy can be excluded as a diagnosis.
- Creatine Kinase (CK) very high, abnormal liver function tests (Alanine Transferase [ALT])
- CK is often extremely elevated in muscular dystrophies. ALT can also be raised; this is not a sign of liver failure but this further indicates muscle breakdown (ALT is produced by damaged muscle and/or liver cells).
The GP tells the family that there seems to be a problem with Freddie’s muscles and she refers Freddie urgently to the paediatric team with expertise in neuromuscular diseases.
- Blood test for DNA analysis (looking for a mutation in the dystrophin gene)
- Screening other family members after genetic counselling
The most likely diagnosis is Duchenne muscular dystrophy. The combination of the red flags in the clinical history and the elevated CK is highly suggestive. DNA testing for mutation in the dystrophin gene will give the diagnosis in most cases.
- X-linked recessive.
- The DMD gene is located on the X chromosome. Boys have one X chromosome and one Y chromosome, girls have two X chromosomes. Women carry the DMD gene but this does not usually cause muscle problems. This is because women have two X chromosomes and the unaffected X chromosome can compensate for the faulty one. In contrast boys only have one X chromosome, therefore cannot compensate for the faulty gene. Boys with the faulty gene will therefore always have symptoms of the condition.
- In about 70% of the cases the condition is passed on from mother to child (in 30% of the cases, there is a new mutation). For a mother carrying the DMD gene, there is a 50% chance she passes on her faulty X chromosome on to her child. That means that if the child is a boy, he has a 50% chance to be affected by Duchenne muscular dystrophy. If it is a girl, she has a 50% chance of being a carrier of Duchenne muscular dystrophy. This is called X-linked inheritance and typically affects single genes.
- Corticosteroids are currently the only medication available that slow the decline in muscle strength (i.e., keep the boys walking for longer), stabilise respiratory function and may protect cardiac function. Steroids are usually started between the ages of 4-8 once muscle function has reached a plateau phase (“steady state”). In this plateau phase it is unlikely that any new motor skills will be acquired. After this the child’s motor skills will gradually start to decline (which may manifest as frequent falls and reduction in walking distance).
