Lumbar punctures (LPs; spinal taps) can provide invaluable information, but only if the local culture allows them to be done and the laboratory can analyze the specimen accurately. In children ≤5 years old, consider using a short small-gauge hypodermic needle; a butterfly needle works well in infants. For children >5 years old, use a standard LP needle, if one is available. Otherwise, use a longer small-gauge hypodermic needle.
Lumbar puncture needles may need to be reused. While this is potentially dangerous, it may be safer to reuse these needles than to reuse hypodermic needles. The obturator allows large material to be cleaned out of the needle’s core. After cleaning, steam autoclave the needles. If that is not possible, high-level disinfection by boiling has been recommended.1 To do this:
Put the needles into a pan and cover them with 3 cm of potable water. Put the lid on the pan and bring the water to a boil. Once it begins to boil, keep it boiling for 15 minutes.
While holding the lid on the pan, pour out the water without letting the needles fall out. This is not as easy as it sounds; practice this before you boil the needles.
Leave the nearly dry needles in the covered pan until they are needed. Never put them anywhere else.
Finding the Midline for a Lumbar Puncture
In resource-poor settings, finding the midline with an ultrasound for an LP may hold the key to success, because there may be no one available to help with a failed LP. In adults, use a curvilinear low-frequency (5 to 2 MHz) transducer to image non-palpable bony landmarks, even if they are deeper than 9 cm. In children, use a linear high-frequency transducer. With a musculoskeletal “preset,” adjust the depth (adults) to 10 to 12 cm and place the probe near the presumed midline with the marker cephalad. Slowly slide the transducer left or right until the facet joints are seen—they look like humps on the ultrasound screen. Then slide the probe caudad until the sacrum is seen as a horizontal hyperechoic line. Use this landmark to identify the L3 to L4 and L4 to L5 interspaces, marking their location on the skin. Then, rotate the transducer 90 degrees to locate the anatomic midline. Slide the probe cephalad and caudad, identifying and marking the spinous processes. Connect the skin markings from the midline and the interspace levels; they will cross at the ideal sites for needle entry. Follow standard LP technique.2
Psychogenic Disorders and Malingering
Patients with psychogenic neurological disorders may present with bizarre motor findings and neurological tests that indicate a functional (psychogenic) disorder. They usually will have normal muscle tone, no atrophy or fasciculations, and no ataxia, although they may try to simulate it. The following are a number ...