2025 – PAGE 402 – NEUROLOGY
HUNTINGTON DISEASE (AKA HUNTINGTON’S DISEASE)
Huntington Disease (aka Huntington’s Disease) is an autosomal dominant disorder due to CAG repeats that can present at any age but usually does so in adulthood. It can show genetic anticipation (severity increases in successive generations, and symptoms start earlier) Key findings include RIGIDITY, HUNTINGTON CHOREA, and EMOTIONAL LABILITY in children. Adults may have dementia and hypotonia.
MNEMONIC: Please see the Genetics section for the autosomal dominant mnemonic. Keep in mind that HUNTINGTON’S inheritance pattern (autosomal dominant) is different than HUNTER’S syndrome (X-linked).
DYSTROPHIES
SPINAL MUSCULAR ATROPHY TYPE I (AKA WERDNIG-HOFFMANN DISEASE)
Spinal Muscular Atrophy Type I (AKA Werdnig-Hoffmann disease) findings include tongue fasciculations, hypotonia, and a poor suck. It’s caused by the degeneration of the anterior horn of the spinal cord, and therefore only disrupts motor function. There are NO sensory deficits. Most affected infants die before one year of age, often from respiratory failure.
PEARLS: There are no tongue fasciculations in kids with Duchenne Muscular Dystrophy or botulism. Also, these children have a NORMAL CK because this is a NERVE problem and NOT a muscle protein problem.
(DOUBLE TAKE) DUCHENNE MUSCULAR DYSTROPHY (DMD)
Duchenne muscular dystrophy is an X-linked disorder (located at Xp21 – low yield) that causes a deficiency in the muscles’ DYSTROPHIN protein. Children are usually wheelchair-bound by 7 or 8 years of age and are unable to walk by their 13th birthday. They can have severe scoliosis, and the major cause of morbidity (and mortality) is the involvement of respiratory muscles. Children have a poor cough and frequent pneumonias. The heart can also be involved (cardiomyopathy). Other symptoms include toe walking, a waddling gait, use of the Gower maneuver to stand, pseudohypertrophy of calf muscles from fatty/fibrous tissue deposition, and poor head control. Start your workup with a CK level (like Dermatomyositis) since it’s ALWAYS elevated. If high, refer to a neurologist for further workup. Electromyogram (EMG) studies can support the diagnosis but are not definitive. Genetic testing (such as multiplex PCR) may provide a definitive diagnosis. If it does not (because of an unknown mutation site), then proceed to a muscle biopsy.
PEARLS: Though it’s an X-linked disorder, there is a very HIGH rate of spontaneous mutations, so the mom does not have to be a carrier, and there does NOT have to be a positive family history. If the mom is a carrier, though, she can have elevated CK levels even though she has no symptoms.
PEARLS: There can be varying degrees of nonprogressive cognitive deficits in children with DMD. So, if a case kind of sounds like DMD and includes mention of some “memory problems or trouble in school” pick DMD.
MNEMONIC: C’mon. Have you ever seen a picture of a female patient doing the Gower maneuver? NO! So of course this is an X-linked disease. Now imagine a child doing the maneuver while wearing a tuX.
MNEMONIC VIDEO: Imagine this kid doing the Gower maneuver in a tuX: www.pbrlinks.com/DUCHENNE1
MYOTONIC DYSTROPHY
Myotonic dystrophy is an autosomal dominant disorder that involves distal weakness, especially in the hands. Look for a history of slow relaxation after contractions. Patients can have endocrine and gastrointestinal problems. The CK is usually normal.