What is the knuckle knuckle dimple knuckle sign?
One of the skeletal abnormalities of Albright’s hereditary osteodystrophy is ‘‘knuckle, knuckle, dimple, dimple’’ appearance of the hand resulting from premature closure of the epiphyses.
This condition is termed as knuckle-dimple sign or Archibald’s sign.
Patients with pseudo hypoparathyroidism type Ia (PHP-1a; autosomal dominant Albright’s hereditary osteodystrophy) may have a skeletal deformity with a short fourth metacarpal.
When they clench their hand to form a fist, a dimple appears where the fourth knuckle should be, emphasizing the short fourth metacarpal bone.
In the ones affected with pseudohypoparathyroidism, the fourth and fifth metacarpal bones are short
In this condition, when the patient make a fist, the knuckles will have dimples at the fourth and fifth positions, therefore they call it “knuckle, knuckle, dimple, dimple”.
In other genetic conditions such as Turner syndrome and in Albright syndrome, it’s usually only the fourth metacarpal is short and therefore they call it knuckle, knuckle, dimple, knuckle.
Brachydactyly is one of the commonly recognized signs of Albright’s hereditary osteodystrophy (AHO), along with short adult stature, obesity and developmental delay.
Short metacarpals are not pathognomonic of AHO and can be seen in many other conditions.
AHO was first described by Albright and his colleagues in 1942. AHO has been genetically linked to GNAS1 gene.
Brachydactyly most commonly involves the fourth and fifth metacarpals, but can also be seen in other metacarpals and metatarsals.
Affected knuckles dimple when the fist is clenched causing the ‘Knuckle–dimple’ sign.
Patients with AHO features can have either pseudohypoparathyroidism or pseudopseudohypoparathyroidism based on the presence of end-organ resistance to parathyroid hormone.
These patients have resistance to parathyroid hormone (low calcium, high phosphorous, high parathyroid hormone), short stature, obesity, ectopic calcifications around weight-bearing joints and paraspinal ligaments, and may have cognitive disabilities.
It is due to a defect in GNAS1 resulting in PTH resistance.
Patients with pseudo-PHP have similar clinical features to PHP-1a, including a short fourth metacarpal (and metatarsal) bone, but lack PTH resistance.