HYPOACTIVE REFLEXES
HYPOACTIVE REFLEXES: Excerpt from Differential Diagnosis in Primary Care
Diffuse hypoactive reflexes are of no significance in otherwise healthy
individuals; however, anatomy is the key to recalling the many
pathologic causes of hypoactive reflexes. Visualizing the reflex arc (see
figure on page 251), we have the spinal cord nerve roots, peripheral nerves,
myoneural junction, and muscle. Now we simply think of the various diseases
that may affect each one of these structures and we have an extensive list
of possibilities.
Spinal cord: Diminished reflexes are seen in poliomyelitis,
syringomyelia, Werdnig–Hoffman syndrome, muscular atrophy, and pernicious
anemia with subacute combined degeneration. Spinal cord concussion,
transection, or hemorrhage may cause hypoactive reflexes at first.
Nerve roots: Diffusely hypoactive reflexes may be found in
Guillain–Barré syndrome and tabes dorsalis, both of which affect the
nerve roots. Focal loss of reflexes may occur in herniated disc, cauda
equina tumor, spinal stenosis, abscess, TB, multiple myeloma, and fracture.
Peripheral nerves: Peripheral neuropathy is associated with diffuse
hypoactive reflexes. There are several causes including alcoholism,
diabetes, drugs, malnutrition, Charcot–Marie–Tooth disease, porphyria,
hereditary hypertrophic neuritis, lead intoxication, and collagen disease.
Focal involvement may be seen in brachial plexus neuritis, sciatic neuritis,
and mononeuritis multiplex.
Myoneural junction: This should bring to mind myasthenia gravis.
Muscle: Generalized decrease in reflexes may be seen in
dermatomyositis, advanced muscular dystrophy, myotonic dystrophica, and
McArdle syndrome.
Approach to the Diagnosis
The differential diagnosis will depend on the presence or absence of
other signs. If there is an acute onset of diffuse hypoactive reflexes and
weakness, poliomyelitis Guillain–Barré syndrome, toxic peripheral
neuropathy, and polymyositis must be considered in the differential. A
gradual onset of diffuse weakness and hypoactive reflexes is more consistent
with muscular atrophy, tabes dorsalis, pernicious anemia, and muscular
dystrophy. Abnormal sensory findings would point to pernicious anemia, tabes
dorsalis, and peripheral neuropathy whereas the absence of abnormal sensory
findings would suggest muscular atrophy, muscular dystrophy, or myasthenia
gravis. Focal loss of reflexes suggests a herniated disc, especially if
there is associated radicular pain. Focal hypoactive reflexes of the lower
extremities require plain films of the lumbosacral spine, EMG and NCV
studies, and an MRI or CT scan of the lumbar spine. Isolated hypoactive
reflexes in the upper extremities require an x-ray of the cervical spine,
MRI of the cervical spine, and NCV and EMG of the upper extremities. Diffuse
hypoactive reflexes merit an extensive laboratory workup including a CBC,
urinalysis, chemistry panel, serum B12 and folic acid, ANA, glucose
tolerance test, blood lead level, urine for porphobilinogen, human
immunodeficiency virus (HIV) antibody titer, and serum protein
electrophoresis. A spinal tap should be done if Guillain–Barré syndrome
is suspected. An EMG and NCV study should also be done if peripheral
neuropathy or muscular dystrophy is suspected. A muscle biopsy may be needed
in muscular dystrophy and dermatomyositis.
Other Useful Tests
-
Anti–double-stranded DNA (lupus)
- Thyroid profile (hypothyroidism)
- Immunoelectrophoresis (macroglobulinemia)
- Kveim test (sarcoidosis)
- Drug screen (drug-induced neuropathy)
- Quantitative urine niacin and thiamine (pellagra, beriberi)
CASE PRESENTATION #51
A 49-year-old white man complained of increasing weakness and fatigue of
all four extremities. Neurologic examination disclosed hypoactive reflexes
in the upper extremities. There were bilateral Babinski signs.
Pictures
Book Source Details
- Book Title: Differential Diagnosis in Primary Care
- Author(s): R. Douglas Collins MD, FACP
- Year of Publication: 2007
- Copyright Details: Differential Diagnosis in Primary Care, Copyright © 2007 Lippincott Williams & Wilkins.
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