So, there is a shortened 4th metacarpal bone that has no relation with recent trauma history. To manifest this finding you can draw a line along the 3d and 5th metacarpal heads this is called my "modified" positive metacarpal sign:
If the 4th metacarpal head intersects with the line, is a negative metacarpal sign. In our case is obviously a positive metacarpal sign as the longitudinal axis of the bone shows isolated restricted development. I called it "modified" because the real measurement is done by drawing a line from the 5th and 4th metacarpal head and is a positive sign when encounters the 3rd metacarpal head. Not too much of a modification but anyways...the real deal is the questions that crossed my mind when I saw this.
My first impression is that could be normal. Maybe a normal but rare variant? And I could be right because literaure says is a normal variant in up to 9.8% of individuals. This tells me that there is a good possibility (almost 90%) that this is a manifestation of a systemic or congenital disease. So therefore we have to search an entity and give differentials to help the patient that maybe unaware of his condition.
Let´s see if this is a congenital malformation. My patient was a mid thirties male patient with no clinical manifestations (apparently) as stated in the history. This almost discharges Turner syndrome as a possibility (as one previous comment kindly suggested), because Turner affects exclusively in women (x-related cromosopathy). It has a wide variety of fenotipic stigmata including isolated 4th metacarpal bone hypoplasia. Another syndrome that has the same manifestations and affects males and females the same is Noonan syndrome. This entity has a normal kariotype unlike Turner's. So should I keep Noonan as a possibility?..maybe but is very rare and the clinical manifestations are striking to avoid. Other congenital abnormality found to develop this type of hypoplasia is Cleido-cranial dysostosis. This is a general skeletal condition so named from the collarbone (cleido-) and cranium deformities which people with it often have. The collarbone or clavicle abnormalities include hypoplasia or aplasia and is manifested as a capability of joining both shoulders in the midline. Cranial deformities include microcephaly with bulging of the forehead, wormian bones, etc. Associated anomalies include supernumerary teeth and deformity of phalanges such as 4th metacarpal hypoplasia. Non congenital causes are more frequently observed and they have to be on the top of my diagnostic possibilities. The most associated is pseudohypoparathyroidism wich is a condition of end organ resistance to the parathormone PTH. Serum levels of PTH are high with low calcium serum level. Other conditions include post-traumatic compicated bode healing and post-infective causes such as Osteomyelitis. Less frequent are sickle cell disease with secondary bone infarction and Gorlin's disease.
My differentials are as listed below:
1. Pseudohypoparathyroidism; recomendation -> correlate with PTH serum levels
2. Normal idiopatic variant.
3. Cleido-cranial dysostosis -> correlate with a screening of clavicle, head, and feet x-ray projections.
As always comments are very welcome!
http://radiopaedia.org/articles/short-4th-5th-metacarpal
Reeder and Felson's gamuts in radiology. Maurice M. Reeder; with MRI gamuts by William G. Bradley, Jr., and ultrasound gamuts by Christopher R. Merritt and input from a distinguished 20-member subspecialty editorial board. New York : Springer, c2003
An evaluation of the metacarpal sign (short fourth metacarpal). Pediatrics. 1970;46 (3): 468-71
Rev Cubana Med 1999;38(2):117-22. Hospital Clinicoquirúrgico "Celia Sánchez Manduley". Manzanillo-Granma. Servicio de Medicina Interna. Disostosis cleido-craneal. Estudio clínico, radiográfico y genético de una familiaDr. César Mustelier Fernández, Dra. Marlenes Chang Lago, Dr. Arturo Luis Almunia Leyva y Dra. Mireille Molero Segrera
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