IS case 540: Isolated bilateral hypoplasia of the 4th metacarpals; pseudopseudohypoparathyroidism
Imaging Sciences URMC 2010
Publication Date: 2010-09-17
History
Patient is a 50-year-old woman presenting with left hand and wrist pain with normal activities of daily living, which includes typing. Previous diagnosis of carpal tunnel syndrome resolved with rest and braces. She had a positive Tinel's sign (parasthesias in the distribution of the median nerve with light percussion of the wrist). Radiographs of the hands were ordered for further evaluation.
Findings
Bilateral hand radiographs were obtained (Figs. 1 & 2). Bilateral isolated hypoplasia/shortening of the 4th metacarpals with normal appearance of other digits including the more distal 4th ray. Bones were otherwise radiographically normal. Mild degenerative changes of the wrist with subtle sclerosis and narrowing of the radiocarpal articulation was also seen.
Diagnosis
Isolated bilateral hypoplasia of the 4th metacarpals; pseudopseudohypoparathyroidism
Discussion
Metacarpal and metatarsal hypoplasia and dysplasia are associated with a number of conditions, congenital and otherwise. This patient presented with a common complaint (suspected recurrence of carpal tunnel syndrome) and radiographs were obtained prior to evaluation by a hand specialist. The finding of isolated bilateral hypoplastic/short 4th metacarpals is incidental and with no other osseous abnormalities the differential diagnoses are severely limited. One condition, pseudopseudohypoparathyroidism (pseudo-PHP) is a variant of a spectrum of syndromes collectively referred to as pseudohypoparathyroidism (PHP). A single protein deficiency (stimulatory G protein, or Gsa) is associated with cAMP production is associated with the syndromes, which may present with PTH-resistant hypocalcemia and hyperphosphatemia in addition to short stature, obesity, mental retardation (50%), rounded facies, dental hypoplasia, and shortened appearance of the metacarpals and metatarsals with predilection for the 4th metacarpals, which constitute PHP. Alternatively, patients may present with the physical manifestations and Gsa deficiency without the more profound hormonal and neurological symptoms and have normal serum calcium and phosphate. This latter constellation is characteristic of pseudo-PHP, and is due to a lesser degree of resistance to PTH and other Gsa-mediated hormone regulatory pathways. This patient is of normal intelligence but has a number of medical co-morbidities (DM2, morbid obesity, hyperlipidemia and hypercholesterolemia, hepatic steatosis), all of which may be influenced by Gsa-mediated hormones.
Alternatively, the finding of isolated 4th metacarpals has been reported, although there is no reported predilection for the 4th metacarpal in these cases and symmetric hypoplasia/shortening is statistically unlikely; however, in the context of normal appearance of the other bones and joints and the absence of more profound dysplasia and evidence of metabolic bone disease, this is a possible consideration. Less likely diagnoses associated with congenitally short metacarpals include Turner syndrome, Noonan syndrome, fetal alcohol syndrome, Poland syndrome, mucopolysaccharidoses, and achondroplasia/hypochondroplasia syndromes.
References
- Wu WI, Schwindinger WF, Aparicio LF, Levine MA. Selective resistance to parathyroid hormone caused by a novel uncoupling mutation in the carboxyl terminus of G alpha(s). A cause of pseudohypoparathyroidism type Ib. J Biol Chem. 2001 Jan 5;276(1):165-71. PMID: 11029463
- Dahnert WF. Radiology Review Manual, 6th ed. Lippincott Williams & Wilkins, 2007.
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